mesa: assert that key->fragprog_inputs_read value isn't too large
mesa: assert that key->fragprog_inputs_read value isn't too large

fragprog_inputs_read is a 12-bit bitfield so check the assigned value.
MSVC warns on the assignment.  Not easy to fix but let's do a sanity check.

Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,metora/MesaGLSLCompiler,jbarczak/glsl-optimizer,bkaradzic/glsl-optimizer,mapbox/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,jbarczak/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,metora/MesaGLSLCompiler,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,zz85/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,metora/MesaGLSLCompiler,mapbox/glsl-optimizer