glsl: Fix constant-folding for reciprocal expressions
glsl: Fix constant-folding for reciprocal expressions

Do not constant-fold a reciprocal if any component of the reciprocated
expression is 0. For example, do not constant-fold `1 / vec4(0, 1, 2, 3)`.

Incorrect, previous behavior
----------------------------
Reciprocals were constant-folded even when some component of the
reciprocated expression was 0. The incorrectly applied arithmetic was:
   1 / 0 := 0
For example,
   1 / vec4(0, 1, 2, 3) = vec4(0, 1, 1/2, 1/3)

NOTE: This is a candidate for the 7.9 and 7.10 branches.

djreep81/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,adobe/glsl2agal,mapbox/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,tokyovigilante/glsl-optimizer,KTXSoftware/glsl2agal,djreep81/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,KTXSoftware/glsl2agal,djreep81/glsl-optimizer,adobe/glsl2agal,mcanthony/glsl-optimizer,mcanthony/glsl-optimizer,metora/MesaGLSLCompiler,KTXSoftware/glsl2agal,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,bkaradzic/glsl-optimizer,adobe/glsl2agal,mcanthony/glsl-optimizer,zz85/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,dellis1972/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,adobe/glsl2agal,benaadams/glsl-optimizer,zeux/glsl-optimizer,jbarczak/glsl-optimizer,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,mapbox/glsl-optimizer,adobe/glsl2agal