glsl: Initialize ast_aggregate_initializer::constructor_type.
glsl: Initialize ast_aggregate_initializer::constructor_type.

Fixes "Uninitialized pointer field" defect reported by Coverity.

Signed-off-by: Vinson Lee <25a259f709b0f1b620605d2518271a846d8826e5@freedesktop.org>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

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