hw/xfree86: fix NULL pointer refrence to mode name

Potentially, the pointer to the mode name could be unset, this can
occur with the xf86-video-nv DDX, in that case there isnt much we can do
except check if the next mode is any better.

Signed-off-by: Yusuf Khan <yusisamerican@gmail.com>
---
(cherry picked from db3aa4e03b)

Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1309>

hw/xfree86/common/xf86Mode.c

@@ -507,6 +507,8 @@ xf86LookupMode(ScrnInfoPtr scrp, DisplayModePtr modep,
             /* scan through the modes in the sort order above */
             if ((p->type & type) != type)
                 continue;
+            if (p->name == NULL)
+                continue;
 
             if (strcmp(p->name, modep->name) == 0) {