localrepo: ignore tags to unknown nodes (issue2750)

mercurial/localrepo.py

@@ -362,7 +362,12 b' class localrepository(repo.repository):'
         tags = {}
         for (name, (node, hist)) in alltags.iteritems():
             if node != nullid:
+                try:
+                    # ignore tags to unknown nodes
+                    self.changelog.lookup(node)
                 tags[encoding.tolocal(name)] = node
+                except error.LookupError:
+                    pass
         tags['tip'] = self.changelog.tip()
         tagtypes = dict([(encoding.tolocal(name), value)
                          for (name, value) in tagtypes.iteritems()])