Fix VEC_COND_EXPR matching with inverted compare

The following fixes detecting of VEC_COND_EXPR <cmp, {0,..}, {-1,...}>
which we recognize in ovce_extract_ops by inverting 'cmp'.  But
after checking that the false value is {-1,...} we then continue
verifying it is also {0,...} which it of course is not.  Fixed
by checking the true value in that case.

	* tree-ssa-reassoc.cc (ovce_extract_ops): Fixup
	false value matching for the inverted comparison case.