Ignore a changed item if it cannot be found in the model

This prevents repeated attempts to reload the data for the non-existing
item. This was the root cause of bug 320791.

Thanks to Hrvoje Senjan and Jekyll Wu for testing the new code and
finding this bug!

BUG: 320791

src/kitemviews/kfileitemmodelrolesupdater.cpp

@@ -1015,6 +1015,7 @@ void KFileItemModelRolesUpdater::updateChangedItems()
         const int index = m_model->index(item);
 
         if (index < 0) {
+            m_changedItems.remove(item);
             continue;
         }