Stop the traceback by re-searching for the list after a deletion. This is the same as songs.

bzr-revno: 1720
Fixes: https://launchpad.net/bugs/820534

openlp/plugins/custom/lib/mediaitem.py

@@ -217,8 +217,7 @@ class CustomMediaItem(MediaManagerItem):
                 for item in self.listView.selectedIndexes()]
             for id in id_list:
                 self.plugin.manager.delete_object(CustomSlide, id)
-            for row in row_list:
-                self.listView.takeItem(row)
+            self.onSearchTextButtonClick()
 
     def onFocus(self):
         self.searchTextEdit.setFocus()