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>