fb: Don't free NULL pixmap in fbCloseScreen. Bug #80313

We fixed fbCloseScreen to use the FreePixmap function so that the
private counts would be updated correctly during CloseScreen. Xvfb
calls FreePixmap and sets devPrivate to NULL before fbCloseScreen is
called; not checking devPrivate before calling would result in a NULL
pointer dereference.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Julien Cristau <jcristau@debian.org>
glamor: Fix stack corruption in glamor_init

glGet on GL_MAX_VIEWPORT_DIMS returns two values

Reviewed-by: Markus Wick <markus@selfnet.de>
Signed-off-by: Keith Packard <keithp@keithp.com>