GL_UNIFORM_BUFFER_SIZE and GL_UNIFORM_BUFFER_START can't be queried
using glGetIntegerv(). They're only valid for glGetInteger64i_v().

This prevents a potential null dereference.

Bug chromium:859775

Change-Id: Ic66f33a582805b021a2d4bd08ff627f704d42aa7
Reviewed-on: https://swiftshader-review.googlesource.com/19748Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>