Charset override for synced IMAP messages only

app/src/main/java/eu/faircode/email/AdapterMessage.java

@@ -5472,6 +5472,9 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
                             message.accountProtocol == EntityAccount.TYPE_POP)
                     .setVisible(message.accountProtocol == EntityAccount.TYPE_IMAP ||
                             EntityFolder.INBOX.equals(message.folderType));
+            popupMenu.getMenu().findItem(R.id.menu_charset)
+                    .setEnabled(message.uid != null)
+                    .setVisible(message.accountProtocol == EntityAccount.TYPE_IMAP);
 
             popupMenu.getMenu().findItem(R.id.menu_alternative)
                     .setTitle(message.isPlainOnly()