Before this fix:
	BACKGROUND threads are not supposed to have connection attributes
	and therefore an ASSERT was in place to make sure this code point
	is not reached from a BACKGROUND thread.
	But when server is started with --thread-handling=no-threads, no
	FOREGROUND thread is created for client connection and this code
	point is reached when a query to table session_connect_attrs is
	made, and an ASSERT was seen.

After this fix:
	Instead of an ASSERT, silently return from the function.