notify: only notify for non-filtered revision

This should fix issue5821 for hook targeting individual revision.

hgext/notify.py

@@ -481,7 +481,7 b' def hook(ui, repo, hooktype, node=None, '
                 ui.pushbuffer()
         if count:
             n.diff(ctx, repo['tip'])
-    else:
+    elif ctx.rev() in repo:
         if not n.node(ctx):
             ui.popbuffer()
             ui.note(_('notify: suppressing notification for merge %d:%s\n') %