Fix crash when playing back a picture with an unknown font.

bug: 5009656
Change-Id: Ic91bdb84e42b4d07f88bd6df1a2bedc2031404df
diff --git a/src/core/SkPicturePlayback.cpp b/src/core/SkPicturePlayback.cpp
index 67b6865..80189ab 100644
--- a/src/core/SkPicturePlayback.cpp
+++ b/src/core/SkPicturePlayback.cpp
@@ -441,7 +441,7 @@
     int typefaceCount = readTagSize(stream, PICT_TYPEFACE_TAG);
     fTFPlayback.setCount(typefaceCount);
     for (i = 0; i < typefaceCount; i++) {
-        fTFPlayback.set(i, SkTypeface::Deserialize(stream))->unref();
+        SkSafeUnref(fTFPlayback.set(i, SkTypeface::Deserialize(stream)));
     }
 
     fPictureCount = readTagSize(stream, PICT_PICTURE_TAG);