The problem was at line 827, where "(qHead - qSize) % 32" could give
unexpected results if qSize > gHead (which wasn't a problem with
unsigned values). Also removed other % operations which could have
cause some issues.

Change-Id: Ia443e05ce1add3879720e90f7dbac771e712d2ab
Reviewed-on: https://swiftshader-review.googlesource.com/12568Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>