st_cb_bitmap: check NULL return from u_upload_alloc
st_cb_bitmap: check NULL return from u_upload_alloc

Signed-off-by: Julien Isorce <341b42cefd783c11d105e1f99b43728d48a9b5d2@oblong.com>
Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler