Fix memory leak in filterRRectToNine

https://codereview.chromium.org/65723005/



git-svn-id: http://skia.googlecode.com/svn/trunk/src@12222 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/effects/SkBlurMaskFilter.cpp b/effects/SkBlurMaskFilter.cpp
index 1769023..34dde3c 100644
--- a/effects/SkBlurMaskFilter.cpp
+++ b/effects/SkBlurMaskFilter.cpp
@@ -333,6 +333,8 @@
         return kFalse_FilterReturn;
     }
 
+    SkAutoMaskFreeImage amf(srcM.fImage);
+
     if (!this->filterMask(&patch->fMask, srcM, matrix, &margin)) {
         return kFalse_FilterReturn;
     }