Xephyr: Check screen resources creation success

If the screen pixmap or the corresponding texture creation with glamor
fails, exit cleanly with an error message instead of segfaulting.

Fixes: https://bugzilla.redhat.com/1431633
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>

hw/kdrive/ephyr/ephyr.c

@@ -725,8 +725,10 @@ ephyrCreateResources(ScreenPtr pScreen)
                            ephyrShadowUpdate, ephyrWindowLinear);
     else {
 #ifdef GLAMOR
-        if (ephyr_glamor)
-            ephyr_glamor_create_screen_resources(pScreen);
+        if (ephyr_glamor) {
+            if (!ephyr_glamor_create_screen_resources(pScreen))
+                return FALSE;
+        }
 #endif
         return ephyrSetInternalDamage(pScreen);
     }

hw/kdrive/ephyr/hostx.c

@@ -1559,13 +1559,18 @@ ephyr_glamor_create_screen_resources(ScreenPtr pScreen)
                                           pScreen->height,
                                           pScreen->rootDepth,
                                           GLAMOR_CREATE_NO_LARGE);
+    if (!screen_pixmap)
+        return FALSE;
 
     pScreen->SetScreenPixmap(screen_pixmap);
     if (pScreen->root && pScreen->SetWindowPixmap)
         TraverseTree(pScreen->root, ephyrSetPixmapVisitWindow, old_screen_pixmap);
 
     /* Tell the GLX code what to GL texture to read from. */
     tex = glamor_get_pixmap_texture(screen_pixmap);
+    if (!tex)
+        return FALSE;
+
     ephyr_glamor_set_texture(scrpriv->glamor, tex);
 
     return TRUE;