GTKUI: Fix Show Zero Hits to only apply to state, owner and tracker_host

There is an issue with the Label plugin where a new label would 'disappear'
and you could not change the options for the new label with zero hits hidden.

deluge/core/filtermanager.py

@@ -223,7 +223,8 @@ class FilterManager(component.Component):
             items["tracker_host"]["Error"] = len(tracker_error_filter(torrent_ids, ("Error",)))
 
         if  not show_zero_hits:
-            for cat in tree_keys:
+            for cat in ["state", "owner", "tracker_host"]:
+                if cat in tree_keys:
                     self._hide_state_items(items[cat])
 
         # Return a dict of tuples: