Fix crash with FontProvider

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

Test: manually done
Change-Id: I81a6f0d295f13bbeb059deafb4283654f97c0090
diff --git a/graphics/java/android/graphics/Typeface.java b/graphics/java/android/graphics/Typeface.java
index 7a7c7af..38e8061 100644
--- a/graphics/java/android/graphics/Typeface.java
+++ b/graphics/java/android/graphics/Typeface.java
@@ -237,6 +237,7 @@
                 IoUtils.closeQuietly(fd);
             }
         }
+        fontFamily.freeze();
         callback.onTypefaceRetrieved(Typeface.createFromFamiliesWithDefault(
                 new FontFamily[] {fontFamily}));
     }