Fix IndexError in asyncio.create_connection with empty exceptions list

Fix IndexError that occurs in asyncio.create_connection() when Happy Eyeballs algorithm leaves empty sublists in the exceptions list, which after flattening becomes an empty list causing str(exceptions[0]) to crash. The fix adds explicit handling for empty exceptions list by changing 'else:' to 'elif len(exceptions) > 1:' and adding a new else clause that raises OSError('create_connection failed') instead of crashing.

Author: heliang666s

Lib/asyncio/base_events.py

@@ -1161,7 +1161,7 @@ async def create_connection(
                         raise ExceptionGroup("create_connection failed", exceptions)
                     if len(exceptions) == 1:
                         raise exceptions[0]
-                    else:
+                    elif len(exceptions) > 1:
                         # If they all have the same str(), raise one.
                         model = str(exceptions[0])
                         if all(str(exc) == model for exc in exceptions):
@@ -1170,6 +1170,9 @@ async def create_connection(
                         # the various error messages.
                         raise OSError('Multiple exceptions: {}'.format(
                             ', '.join(str(exc) for exc in exceptions)))
+                    else:
+                        # No exceptions were collected, raise a generic connection error
+                        raise OSError('create_connection failed')
                 finally:
                     exceptions = None