fix(thread-list): Prevent empty state from showing when loading list

- EmptyState should only be displayed when the thread-list is actually
empty, not while it is being loaded
- Update ObservableListDataSource to have a state of loaded only when
the requested range is > 0, i.e. when we are actually requesting threads

src/flux/stores/observable-list-data-source.coffee

@@ -44,7 +44,7 @@ class ObservableListDataSource extends ListTabular.DataSource
     @_countEstimate
 
   loaded: ->
-    @_resultSet isnt null
+    @_resultSet isnt null and @_resultDesiredLast > 0
 
   empty: =>
     not @_resultSet or @_resultSet.empty()