Fix "Loading.../Loading..." in caption

BUG: 259210
(cherry picked from commit 39aa2c85783b2381ad7fa199ee1ee028a32c2c54)

kmmainwidget.cpp

@@ -511,6 +511,9 @@ void KMMainWidget::slotCollectionFetched( int collectionId )
     mCurrentFolder->setCollection( MailCommon::Util::updatedCollection( mCurrentFolder->collection() ) );
     updateMessageActions();
     updateFolderMenu();
+  }
+  // We call this for any collection, it could be one of our parents...
+  if ( mCurrentFolder ) {
     emit captionChangeRequest( MailCommon::Util::fullCollectionPath( mCurrentFolder->collection() ) );
   }
 }