mesa: choose GLSL vertex shader over ARB/internal vertex program in get_fp_input_mask()

mesa: choose GLSL vertex shader over ARB/internal vertex program in get_fp_input_mask()

This is a work-around the for the fact that we do fragment shader state
validation before vertex shader validation (see comments in state.c) so in
get_fp_input_mask() we can't rely on ctx->VertexProgram._Current being up to
date yet.

This fixes a glean glsl1 test failure.