mesa/main: simplify _mesa_IsRenderbuffer()
mesa/main: simplify _mesa_IsRenderbuffer()

_mesa_lookup_renderbuffer() already checks if 'id' is non-zero.

Signed-off-by: Samuel Pitoiset <506e97eed81d9e59d22f4c73fb51123bb62b4a30@gmail.com>
Reviewed-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler