main: create_buffers unlocks mutex when throwing OUT_OF_MEMORY.
main: create_buffers unlocks mutex when throwing OUT_OF_MEMORY.

Ilia Mirkin found that I had forgotten to free the mutex in the error case.

Reviewed-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler