view,list: fix crash when viewing incomplete imap messages

With IMAP, due to an unidentified reason, some messages to not have any
body accessible. When viewing them, aerc crashes:

  git.sr.ht/~sircmpwn/aerc/lib.usePGP
          lib/messageview.go:37
  git.sr.ht/~sircmpwn/aerc/lib.NewMessageStoreView
          lib/messageview.go:67
  git.sr.ht/~sircmpwn/aerc/commands/account.ViewMessage.Execute
          commands/account/view.go:45
  git.sr.ht/~sircmpwn/aerc/commands.(*Commands).ExecuteCommand
          commands/commands.go:66
  main.execCommand
          aerc.go:61
  main.main.func2
          aerc.go:160
  aerc crashed: runtime error: invalid memory address or nil pointer
  dereference

Check the pointer before dereferencing.

Also, add a global check in ParseMessageFormat where a similar issue may
occur.

Signed-off-by: Robin Jarry <robin@jarry.cc>

lib/format/format.go

@@ -58,6 +58,10 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 	}
 
 	envelope := ctx.MsgInfo.Envelope
+	if envelope == nil {
+		return "", nil,
+			errors.New("no envelope available for this message")
+	}
 
 	var c rune
 	for i, ni := 0, 0; i < len(format); {
@@ -105,10 +109,6 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 		case '%':
 			retval = append(retval, '%')
 		case 'a':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.From) == 0 {
 				return "", nil,
 					errors.New("found no address for sender")
@@ -117,10 +117,6 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			retval = append(retval, 's')
 			args = append(args, addr.Address)
 		case 'A':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			var addr *mail.Address
 			if len(envelope.ReplyTo) == 0 {
 				if len(envelope.From) == 0 {
@@ -156,10 +152,6 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 				dummyIfZeroDate(date.Local(),
 					timeFmt, thisDayTimeFmt, thisYearTimeFmt))
 		case 'f':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.From) == 0 {
 				return "", nil,
 					errors.New("found no address for sender")
@@ -168,10 +160,6 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			retval = append(retval, 's')
 			args = append(args, addr)
 		case 'F':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.From) == 0 {
 				return "", nil,
 					errors.New("found no address for sender")
@@ -196,17 +184,9 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			args = append(args, strings.Join(ctx.MsgInfo.Labels, ", "))
 
 		case 'i':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			retval = append(retval, 's')
 			args = append(args, envelope.MessageId)
 		case 'n':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.From) == 0 {
 				return "", nil,
 					errors.New("found no address for sender")
@@ -221,33 +201,17 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			retval = append(retval, 's')
 			args = append(args, val)
 		case 'r':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			addrs := FormatAddresses(envelope.To)
 			retval = append(retval, 's')
 			args = append(args, addrs)
 		case 'R':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			addrs := FormatAddresses(envelope.Cc)
 			retval = append(retval, 's')
 			args = append(args, addrs)
 		case 's':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			retval = append(retval, 's')
 			args = append(args, envelope.Subject)
 		case 't':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.To) == 0 {
 				return "", nil,
 					errors.New("found no address for recipient")
@@ -259,10 +223,6 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			retval = append(retval, 's')
 			args = append(args, ctx.AccountName)
 		case 'u':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.From) == 0 {
 				return "", nil,
 					errors.New("found no address for sender")
@@ -275,10 +235,6 @@ func ParseMessageFormat(format string, timeFmt string, thisDayTimeFmt string,
 			retval = append(retval, 's')
 			args = append(args, mailbox)
 		case 'v':
-			if envelope == nil {
-				return "", nil,
-					errors.New("no envelope available for this message")
-			}
 			if len(envelope.From) == 0 {
 				return "", nil,
 					errors.New("found no address for sender")

lib/messageview.go

@@ -34,6 +34,9 @@ type MessageView interface {
 }
 
 func usePGP(info *models.BodyStructure) bool {
+	if info == nil {
+		return false
+	}
 	if info.MIMEType == "application" {
 		if info.MIMESubType == "pgp-encrypted" ||
 			info.MIMESubType == "pgp-signature" {