Fix three problems

1) user-defined tag categories broke when the custom column behind an item was removed
2) get_categories was called with an incorrect search restriction string. The 'search:' was missing.
3) changing from a restriction that matched nothing to one that matched some books incorrectly rebuilt the tags list (order of signals problem)

src/calibre/gui2/dialogs/tag_categories.py

@@ -71,12 +71,16 @@ class TagCategories(QDialog, Ui_TagCategories):
             for item,l in enumerate(self.categories[cat]):
                 key = ':'.join([l[1], l[0]])
                 t = self.all_items_dict.get(key, None)
+                if l[1] in self.category_labels:
                     if t is None:
                         t = Item(name=l[0], label=l[1], index=len(self.all_items),
                                  icon=category_icons[self.category_labels.index(l[1])], exists=False)
                         self.all_items.append(t)
                         self.all_items_dict[key] = t
                     l[2] = t.index
+                else:
+                    # remove any references to a category that no longer exists
+                    del self.categories[cat][item]
 
         self.all_items_sorted = sorted(self.all_items, cmp=lambda x,y: cmp(x.name.lower(), y.name.lower()))
         self.display_filtered_categories(0)

src/calibre/gui2/library.py

@@ -1077,7 +1077,7 @@ class BooksView(TableView):
 
     def connect_to_restriction_set(self, tv):
         QObject.connect(tv, SIGNAL('restriction_set(PyQt_PyObject)'),
-                        self._model.set_search_restriction)
+                        self._model.set_search_restriction) # must be synchronous (not queued)
 
     def connect_to_book_display(self, bd):
         QObject.connect(self._model, SIGNAL('new_bookdisplay_data(PyQt_PyObject)'),

src/calibre/gui2/tag_view.py

@@ -64,10 +64,10 @@ class TagsView(QTreeView):
         if len(s) == 0:
             self.search_restriction = ''
         else:
-            self.search_restriction = unicode(s)
+            self.search_restriction = 'search:"%s"' % unicode(s).strip()
         self.model().set_search_restriction(self.search_restriction)
-        self.recount()
         self.emit(SIGNAL('restriction_set(PyQt_PyObject)'), self.search_restriction)
+        self.recount() # Must happen after the emission of the restriction_set signal
         self.emit(SIGNAL('tags_marked(PyQt_PyObject, PyQt_PyObject)'),
                          self._model.tokens(), self.match_all)
 
@@ -264,7 +264,7 @@ class TagsModel(QAbstractItemModel):
         for c in self.user_categories:
             l = []
             for (name,label,ign) in self.user_categories[c]:
-                if name in taglist[label]: # use same node as the complete category
+                if label in taglist and name in taglist[label]: # use same node as the complete category
                     l.append(taglist[label][name])
                 # else: do nothing, to eliminate nodes that have zero counts
             if config['sort_by_popularity']:

src/calibre/library/caches.py

@@ -543,4 +543,4 @@ class ResultCache(SearchQueryParser):
         return []
 
     def set_search_restriction(self, s):
-        self.search_restriction = '' if not s else 'search:"%s"' % (s.strip())
+        self.search_restriction = s