present/scmd: Check that the flip and screen pixmap pitches match

If they don't, flipping will result in corrupted display.

Test case:

* Run Xorg at 1920x1080 with no window manager
* glxgears -geometry 2048x1080

present/present_scmd.c

@@ -78,7 +78,7 @@ present_check_flip(RRCrtcPtr            crtc,
                    PresentFlipReason   *reason)
 {
     ScreenPtr                   screen = window->drawable.pScreen;
-    PixmapPtr                   window_pixmap;
+    PixmapPtr                   screen_pixmap, window_pixmap;
     WindowPtr                   root = screen->root;
     present_screen_priv_ptr     screen_priv = present_screen_priv(screen);
 
@@ -99,8 +99,9 @@ present_check_flip(RRCrtcPtr            crtc,
         return FALSE;
 
     /* Make sure the window hasn't been redirected with Composite */
+    screen_pixmap = screen->GetScreenPixmap(screen);
     window_pixmap = screen->GetWindowPixmap(window);
-    if (window_pixmap != screen->GetScreenPixmap(screen) &&
+    if (window_pixmap != screen_pixmap &&
         window_pixmap != screen_priv->flip_pixmap &&
         window_pixmap != present_flip_pending_pixmap(screen))
         return FALSE;
@@ -126,7 +127,8 @@ present_check_flip(RRCrtcPtr            crtc,
         window->drawable.x != pixmap->screen_x || window->drawable.y != pixmap->screen_y ||
 #endif
         window->drawable.width != pixmap->drawable.width ||
-        window->drawable.height != pixmap->drawable.height) {
+        window->drawable.height != pixmap->drawable.height ||
+        pixmap->devKind != screen_pixmap->devKind) {
         return FALSE;
     }