fix: crash when copying/moving all messages

This prevents dereferencing nil when updating RUE counts. This seems to
happen for messages that were not yet loaded, but were selected for
copy operation. This can happen when using `mark -a` command and then
initiating copy operation.

When such message is encountered during RUE counting, it is stopped
and full recount is triggered.

**Original backtrace:**
Error: runtime error: invalid memory address or nil pointer dereference

goroutine 1 [running]:
runtime/debug.Stack()
	runtime/debug/stack.go:24 +0x65
git.sr.ht/~rjarry/aerc/logging.PanicHandler()
	git.sr.ht/~rjarry/aerc/logging/panic-logger.go:45 +0x64b
panic({0x9e5f80, 0xecc360})
	runtime/panic.go:844 +0x258
git.sr.ht/~rjarry/aerc/widgets.(*AccountView).onMessage(0xc0001be870, {0xb7f860?, 0xc00073b4c0?})
	git.sr.ht/~rjarry/aerc/widgets/account.go:353 +0xecc
git.sr.ht/~rjarry/aerc/widgets.(*AccountView).Tick(0xc0001be870)
	git.sr.ht/~rjarry/aerc/widgets/account.go:116 +0x6c
git.sr.ht/~rjarry/aerc/widgets.(*Aerc).Tick(0xc0003ba000)
	git.sr.ht/~rjarry/aerc/widgets/aerc.go:144 +0x7a
main.main()
	git.sr.ht/~rjarry/aerc/aerc.go:225 +0xbb8

Signed-off-by: Ensar Sarajčić <dev@ensarsarajcic.com>
Acked-by: Robin Jarry <robin@jarry.cc>

widgets/account.go

@@ -334,12 +334,18 @@ func (acct *AccountView) onMessage(msg types.WorkerMessage) {
 		// Only update the destination destStore if it is initialized
 		if destStore, ok := acct.dirlist.MsgStore(msg.Destination); ok {
 			var recent, unseen int
+			var accurate bool = true
 			for _, uid := range msg.Uids {
 				// Get the message from the originating store
 				msg, ok := acct.Store().Messages[uid]
 				if !ok {
 					continue
 				}
+				// If message that was not yet loaded is copied
+				if msg == nil {
+					accurate = false
+					break
+				}
 				seen := false
 				for _, flag := range msg.Flags {
 					if flag == models.SeenFlag {
@@ -353,13 +359,19 @@ func (acct *AccountView) onMessage(msg types.WorkerMessage) {
 					unseen = unseen + 1
 				}
 			}
-			destStore.DirInfo.Recent += recent
-			destStore.DirInfo.Unseen += unseen
-			destStore.DirInfo.Exists += len(msg.Uids)
-			// True. For imap, we don't have the message in the store until we
-			// Select so we need to rely on the math we just did for accurate
-			// counts
-			destStore.DirInfo.AccurateCounts = true
+			if accurate {
+				destStore.DirInfo.Recent += recent
+				destStore.DirInfo.Unseen += unseen
+				destStore.DirInfo.Exists += len(msg.Uids)
+				// True. For imap, we don't have the message in the store until we
+				// Select so we need to rely on the math we just did for accurate
+				// counts
+				destStore.DirInfo.AccurateCounts = true
+			} else {
+				destStore.DirInfo.Exists += len(msg.Uids)
+				// False to trigger recount of recent/unseen
+				destStore.DirInfo.AccurateCounts = false
+			}
 		}
 	case *types.LabelList:
 		acct.labels = msg.Labels