Proposed fix for crash in Cr70244.

git-svn-id: http://skia.googlecode.com/svn/trunk@764 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index faf030c..b05d424 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -991,6 +991,10 @@
     antialiasing (worst case)
  */
 bool SkCanvas::quickReject(const SkRect& rect, EdgeType et) const {
+
+    if (!rect.hasValidCoordinates())
+        return true;
+
     if (fMCRec->fRegion->isEmpty()) {
         return true;
     }