xwayland: Don't load extension list more than once

When running an Xwayland server from the command line, we end up
resetting the server every time all of the clients connected to the
server leave. This would be fine, except that xwayland makes the mistake
of unconditionally calling LoadExtensionList(). This causes us to setup
the glxExtension twice in a row which means that when we lose our last
client on the second server generation, we end up trying to call the glx
destructors twice in a row resulting in a segfault:

(EE)
(EE) Backtrace:
(EE) 0: Xwayland (OsSigHandler+0x3b) [0x4982f9]
(EE) 1: /lib64/libpthread.so.0 (__restore_rt+0x0) [0x70845bf]
(EE) 2: /usr/lib64/dri/swrast_dri.so (__driDriverGetExtensions_virtio_gpu+0x32897d) [0x1196e5bd]
(EE) 3: /usr/lib64/dri/swrast_dri.so (__driDriverGetExtensions_virtio_gpu+0x328a45) [0x1196e745]
(EE) 4: /usr/lib64/dri/swrast_dri.so (__driDriverGetExtensions_virtio_gpu+0x32665f) [0x11969f7f]
(EE) 5: Xwayland (__glXDRIscreenDestroy+0x30) [0x54686e]
(EE) 6: Xwayland (glxCloseScreen+0x3f) [0x5473db]
(EE) 7: Xwayland (glxCloseScreen+0x53) [0x5473ef]
(EE) 8: Xwayland (dix_main+0x7b6) [0x44c8c9]
(EE) 9: Xwayland (main+0x28) [0x61c503]
(EE) 10: /lib64/libc.so.6 (__libc_start_main+0xf1) [0x72b1401]
(EE) 11: Xwayland (_start+0x2a) [0x4208fa]
(EE) 12: ? (?+0x2a) [0x2a]
(EE)
(EE) Segmentation fault at address 0x18
(EE)
Fatal server error:
(EE) Caught signal 11 (Segmentation fault). Server aborting
(EE)

Easy reproduction recipe:
- Start an Xwayland session with the default settings
- Open a window
- Close that window
- Open another window
- Close that window
- Total annihilation occurs

Signed-off-by: Lyude <lyude@redhat.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

hw/xwayland/xwayland.c

@@ -1013,8 +1013,9 @@ InitOutput(ScreenInfo * screen_info, int argc, char **argv)
     screen_info->bitmapBitOrder = BITMAP_BIT_ORDER;
     screen_info->numPixmapFormats = ARRAY_SIZE(depths);
 
-    LoadExtensionList(xwayland_extensions,
-                      ARRAY_SIZE(xwayland_extensions), FALSE);
+    if (serverGeneration == 1)
+        LoadExtensionList(xwayland_extensions,
+                          ARRAY_SIZE(xwayland_extensions), FALSE);
 
     /* Cast away warning from missing printf annotation for
      * wl_log_func_t.  Wayland 1.5 will have the annotation, so we can