Do not raise an error if no VM is selected for remote GNS3 VM

gns3server/controller/gns3vm/remote_gns3_vm.py

@@ -51,6 +51,8 @@ class RemoteGNS3VM(BaseGNS3VM):
         Starts the GNS3 VM.
         """
 
+        if not self.vmname:
+            return
         vm_compute = None
         for compute in self._controller.computes.values():
             if compute.name == self.vmname: