Fix an uninitialized variable spotted by valgrind

Apparently if the program is 0 the NVIDIA drivers don't write anything
in the glGetIntegerv argument (!), causing it to be left uninitialized.

Change-Id: I159784569faa20ed7d2af50c6c4fabceabed46c9
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>