gfxlib2: Fix read-after-free in X11 OpenGL driver_init()

XFree(info) shouldn't be called before the fb_hX11Init() call which
accesses info->depth in its argument list.
gfxlib2: Check glXCreateContext() result with != 0 instead of > 0

According to man pages found on the web, glXCreateContext() returns NULL
on failure. Also, the GLXContext it returns is a pointer type. Thus != 0
should be better than > 0, and casting to intptr_t and then comparing > 0
especially seems weird since that could cause non-NULL values to be
rejected because they appear to be < 0 (address values > 2GiB wrapping
around/overflowing).