safely handle null blur filter



git-svn-id: http://skia.googlecode.com/svn/trunk@3629 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/samplecode/SampleAnimBlur.cpp b/samplecode/SampleAnimBlur.cpp
index 74f8811..7f077e6 100644
--- a/samplecode/SampleAnimBlur.cpp
+++ b/samplecode/SampleAnimBlur.cpp
@@ -50,7 +50,7 @@
                                        gStyles[i],
                                        SkBlurMaskFilter::kHighQuality_BlurFlag);
             SkPaint paint;
-            paint.setMaskFilter(mf)->unref();
+            SkSafeUnref(paint.setMaskFilter(mf));
             paint.setColor(random.nextU() | 0xff000000);
             canvas->drawCircle(200 * SK_Scalar1 + 400 * (i % 2) * SK_Scalar1,
                                200 * SK_Scalar1 + i / 2 * 400 * SK_Scalar1,