am 31a69fdb: throw if we have a null typeface native instance (so we don\'t...

am 31a69fdb: throw if we have a null typeface native instance (so we don\'t crash in native code) we may still have to native-destroy a Typeface with a null ref, so check for that

Merge commit '31a69fdb' into eclair-mr2-plus-aosp

* commit '31a69fdb':
  throw if we have a null typeface native instance (so we don't crash in native code)