mesa: Call _mesa_test_texobj_completeness() before using _MaxLevel in image validation.
mesa: Call _mesa_test_texobj_completeness() before using _MaxLevel in image validation.

gl_texture_object::_MaxLevel doesn't have any meaningful value until
_mesa_test_texobj_completeness() has been run.  Fixes the "level"
ARB_shader_image_load_store piglit test.

Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler