bug fixed that add extra space in QEMU command when there is no network to be attached

uncloud/host/virtualmachine.py

@@ -153,7 +153,10 @@ class VM:
                 )
             )
 
-        return command.split(" ")
+        if command:
+            command = command.split(' ')
+
+        return command
 
     def delete_network_dev(self):
         try: