Fix WhatsAppChatLoader regex pattern for 24 hour time format (langchain-ai#2458)

Fix for 24 hour time format bug. Now whatsapp regex is able to parse either 12 or 24 hours time format. Linked [issue](langchain-ai#2457).

Author: itortouch

langchain/document_loaders/whatsapp_chat.py

@@ -28,7 +28,7 @@ def load(self) -> List[Document]:
 
  for line in lines:
  result = re.match(
- r"(\d{1,2}/\d{1,2}/\d{2,4}, \d{1,2}:\d{1,2} (?:AM|PM)) - (.*?): (.*)",
+ r"(\d{1,2}/\d{1,2}/\d{2,4}, \d{1,2}:\d{1,2}(?: AM| PM)?) - (.*?): (.*)",
  line.strip(),
  )
  if result: