If we are going to use get_first_fn let's make sure we operate on
is_overloaded_fn, as the rest of the codebase does, and if lookup finds
any class-scope declaration, return early too.

	PR c++/93597 - ICE with lambda in operator function.
	* name-lookup.c (maybe_save_operator_binding): Check is_overloaded_fn.

	* g++.dg/cpp0x/lambda/lambda-93597.C: New test.