notice if the bitmap failed to load



git-svn-id: http://skia.googlecode.com/svn/trunk@1804 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/samplecode/SampleImageDir.cpp b/samplecode/SampleImageDir.cpp
index 8ef59ad..e7ab634 100644
--- a/samplecode/SampleImageDir.cpp
+++ b/samplecode/SampleImageDir.cpp
@@ -29,6 +29,10 @@
     SkMatrix m;
 
     SkImageDecoder::DecodeFile("/Users/reed/Downloads/3elfs.jpg", &bitmap);
+    if (!bitmap.pixelRef()) {
+        return;
+    }
+
     SkShader* s = SkShader::CreateBitmapShader(bitmap,
                                                SkShader::kRepeat_TileMode,
                                                SkShader::kRepeat_TileMode);