fix: use better assumptions for images_received

The presence of the key `output` in `data` during `send_sync` calls was enough to assert `data["output"]["images"]` was present and populated (i.e., we are post-inference and receiving the final images from comfyui). However, comfyui internals have changed so that `data["output"]["images"]` can be equal to `None` in ordinary circumstances during other stages of generation. As such, I have changed the logic to check for the key and for non-`None` values.

hordelib/comfy_horde.py

@@ -650,8 +650,15 @@ def reconnect_input(cls, dct, input, output):
     # This is the callback handler for comfy async events.
     def send_sync(self, label: str, data: dict, _id: str) -> None:
         # Get receive image outputs via this async mechanism
-        if "output" in data and "images" in data["output"]:
-            images_received = data["output"]["images"]
+        output = data.get("output", None)
+        images_received = None
+        if output is not None and "images" in output:
+            images_received = output.get("images", None)
+
+        if images_received is not None:
+            if len(images_received) == 0:
+                logger.warning("Received no output images from comfyui")
+
             for image_info in images_received:
                 if not isinstance(image_info, dict):
                     logger.error(f"Received non dict output from comfyui: {image_info}")