vnc: handle case where tag vncport in invalid

cccli/commands/vnc.py

@@ -87,7 +87,10 @@ class Command_vnc(TqlCommand):
             raise cmdError("No selected object")
         for vm in ans["objects"]:
             host_id = vm["p"]
-            dest_port = int(vm["vncport"])
+            try:
+                dest_port = int(vm["vncport"])
+            except ValueError:
+                raise cmdError('Invalid value for tag vncport')
             # check if we have the right to forward on this hypervisor
             ans2 = self.rpc.call("list", "id:%s" % host_id, method="forward")
             if len(ans2["objects"]) == 0: