Correctly free resouces bound to scripts when the scripts are deleted.

Change-Id: Idfcc30f1a7de0badeb6d8254ed508938d89f4070
b: 3381615
diff --git a/rsFont.h b/rsFont.h
index 00d77c8..4820999 100644
--- a/rsFont.h
+++ b/rsFont.h
@@ -119,6 +119,7 @@
     Font(Context *rsc);
     bool init(const char *name, float fontSize, uint32_t dpi, const void *data = NULL, uint32_t dataLen = 0);
 
+    virtual void preDestroy() const;
     FT_Face mFace;
     bool mInitialized;
     bool mHasKerning;