swr: [rasterizer core] Fix RECT_LIST primitive assembly
swr: [rasterizer core] Fix RECT_LIST primitive assembly

The bug would make the 3rd component of attributes on the second
triangle of a RECT be invalid.

Reviewed-by: Bruce Cherniak <a5345730962d952f474b19e983398300e1cb5f29@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler