Check swipe target

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

@@ -761,7 +761,9 @@ public class FragmentMessages extends FragmentBase {
                         db.beginTransaction();
 
                         EntityFolder target = db.folder().getFolder(tid);
-                        if (target != null) {
+                        if (target == null)
+                            throw new IllegalArgumentException(context.getString(R.string.title_no_folder));
+
                         EntityAccount account = db.account().getAccount(target.account);
                         EntityMessage message = db.message().getMessage(id);
                         if (message != null) {
@@ -774,7 +776,6 @@ public class FragmentMessages extends FragmentBase {
                                 db.message().setMessageUiIgnored(threaded.id, true);
                             }
                         }
-                        }
 
                         db.setTransactionSuccessful();
                     } finally {

app/src/main/res/values/strings.xml

@@ -328,6 +328,7 @@
     <string name="title_no_stream">An outdated app sent a file path instead of a file stream</string>
     <string name="title_no_contacts">Contact picker not available</string>
     <string name="title_no_internet">No internet connection</string>
+    <string name="title_no_folder">Folder does not exist</string>
     <string name="title_accross_remark">Messages moved across accounts will be downloaded again resulting in extra data usage</string>
     <string name="title_raw_saved">Raw message saved</string>
     <string name="title_attachment_saved">Attachment saved</string>