vrend: handle glsl version query failures as fatal
Occasionally (on Intel GLK Chromebooks) we see crashes due to SEGFAULT'd
reads in in sscanf during glsl version querying. These are quite rare,
but with a consistent rate across ChromeOS releases.
This change changes the crash into a fatal runtime error, while the root
cause is investigated.
Signed-off-by: Ryan Neph <ryanneph@google.com>