mesa/glthread: Call unmarshal_batch directly in glthread_finish
mesa/glthread: Call unmarshal_batch directly in glthread_finish

Call it directly when batch queue is empty. This avoids costly thread
synchronisation. This commit improves performance of games that have
previously regressed with mesa_glthread=true.

Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler