glsl/blob: Return false from ensure_can_read on overrun

Otherwise, if you have a large read fail and then try to do a small
read, the small read may succeed even though it's at the wrong offset.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: mesa-stable@lists.freedesktop.org
1 file changed