glsl: fix explicit location validation for doubles
glsl: fix explicit location validation for doubles

Previously we would fail to find a match for the second half of a
dvec4 as 'i' would get incremented to 1 before we added the var to
the array at component 0.

Reviewed-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler