Merge pull request #941 from guokeno0/master

fix toposerver to tolerate nil return from GetEndPoints()

go/vt/vtgate/srv_topo_server.go

@@ -411,7 +411,7 @@ func (server *ResilientSrvTopoServer) GetEndPoints(ctx context.Context, cell, ke
 			server.endPointCounters.errors.Add(key, 1)
 			return
 		}
-		if len(result.Entries) == 0 {
+		if result == nil || len(result.Entries) == 0 {
 			server.endPointCounters.emptyResults.Add(key, 1)
 			return
 		}