Langchain_community: Small Fix when loading facebook messages (#15358)

- **Description:** SingleFileFacebookMessengerChatLoader did not handle
the case for when messages had stickers and/or photos so fixed that.
  - **Issue:** #15356

---------

Co-authored-by: Harrison Chase <[email protected]>

libs/community/langchain_community/chat_loaders/facebook_messenger.py

@@ -37,7 +37,13 @@ def lazy_load(self) -> Iterator[ChatSession]:
             data = json.load(f)
         sorted_data = sorted(data["messages"], key=lambda x: x["timestamp_ms"])
         messages = []
-        for m in sorted_data:
+        for index, m in enumerate(sorted_data):
+            if "content" not in m:
+                logger.info(
+                    f"""Skipping Message No.
+                    {index+1} as no content is present in the message"""
+                )
+                continue
             messages.append(
                 HumanMessage(
                     content=m["content"], additional_kwargs={"sender": m["sender_name"]}