Fix crash with FontProvider

Need to freeze the FontFamily otherwise the FontFamily is not created.

Test: manually done
Change-Id: I81a6f0d295f13bbeb059deafb4283654f97c0090

graphics/java/android/graphics/Typeface.java

@@ -237,6 +237,7 @@ public class Typeface {
                 IoUtils.closeQuietly(fd);
             }
         }
+        fontFamily.freeze();
         callback.onTypefaceRetrieved(Typeface.createFromFamiliesWithDefault(
                 new FontFamily[] {fontFamily}));
     }