[Bugfix] Fix port handling in make_zmq_path (vllm-project#19117)

Signed-off-by: minpeter <kali2005611@gmail.com>

Author: mgoin

vllm/utils.py

@@ -2461,7 +2461,7 @@ def make_zmq_path(scheme: str, host: str, port: Optional[int] = None) -> str:
     Returns:
         A properly formatted ZMQ path string.
     """
-    if not port:
+    if port is None:
         return f"{scheme}://{host}"
     if is_valid_ipv6_address(host):
         return f"{scheme}://[{host}]:{port}"