render: Propagate allocation failure from createSourcePicture()

All the callers were already checking for failure, except that
createSourcePicture() itself was failing to check whether it
successfully allocated the Picture.

[ajax: Rebase, fix line wrap of preceding line]

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jeremy Huddleston <jeremyhu@apple.com>

render/picture.c

@@ -862,7 +862,11 @@ createSourcePicture(void)
 {
     PicturePtr pPicture;
 
-    pPicture = dixAllocateScreenObjectWithPrivates(NULL, PictureRec, PRIVATE_PICTURE);
+    pPicture = dixAllocateScreenObjectWithPrivates(NULL, PictureRec,
+                                                   PRIVATE_PICTURE);
+    if (!pPicture)
+	return 0;
+
     pPicture->pDrawable = 0;
     pPicture->pFormat = 0;
     pPicture->pNext = 0;