tree-optimization/116241 - ICE with SLP condition reduction

When there's a conversion in front of a SLP condition reduction the
code following the reduc-idx SLP chain fails because it assumes
there's only COND_EXPRs.

	PR tree-optimization/116241
	* tree-vect-loop.cc (vect_create_epilog_for_reduction): Handle
	non-COND_EXPR nodes in SLP reduction chain following.

	* g++.dg/vect/pr116241.cc: New testcase.