msgpart: factorize mime type and filename construction

Reduce code duplication.

Signed-off-by: Robin Jarry <robin@jarry.cc>
Acked-by: Moritz Poldrack <moritz@poldrack.dev>

commands/msg/forward.go

@@ -198,7 +198,7 @@ func (forward) Execute(aerc *widgets.Aerc, args []string) error {
 						continue
 					}
 					store.FetchBodyPart(msg.Uid, p, func(reader io.Reader) {
-						mime := fmt.Sprintf("%s/%s", bs.MIMEType, bs.MIMESubType)
+						mime := bs.FullMIMEType()
 						params := lib.SetUtf8Charset(bs.Params)
 						name, ok := params["name"]
 						if !ok {

commands/msg/recall.go

@@ -204,7 +204,7 @@ func (Recall) Execute(aerc *widgets.Aerc, args []string) error {
 						continue
 					}
 					msg.FetchBodyPart(p, func(reader io.Reader) {
-						mime := fmt.Sprintf("%s/%s", bs.MIMEType, bs.MIMESubType)
+						mime := bs.FullMIMEType()
 						params := lib.SetUtf8Charset(bs.Params)
 						name, ok := params["name"]
 						if !ok {

commands/msg/reply.go

@@ -326,7 +326,7 @@ func addMimeType(msg *models.MessageInfo, part []int,
 	if err != nil {
 		return err
 	}
-	orig.MIMEType = fmt.Sprintf("%s/%s", bs.MIMEType, bs.MIMESubType)
+	orig.MIMEType = bs.FullMIMEType()
 	return nil
 }