Fix incomplete check of input params in blorp_surf_convert_to_uncompressed()
which can lead to NULL pointer dereferencing.
Fixes: 5ae8043fed ("intel/blorp: Add an entrypoint for doing
bit-for-bit copies")
Fixes: f395d0abc8 ("intel/blorp: Internally expose
surf_convert_to_uncompressed")
Reviewed-by: Emil Velikov <emli.velikov@collabora.com>
Reviewed-by: Andres Gomez <agomez@igalia.com>