Failing Text-To-Speech CTS tests fix.

Fix for failing android.speech.tts.cts.TextToSpeechServiceTest#testSynthesizeToFile.
In test env, ParcelFileDescriptor instance may be EXACTLY the same one that client uses.
And if it's closed by a client, then service is prevented from writing anything to the output.

Bug: 8377754
Change-Id: I7f95aae1b877e543ab02d3c548b29537aa852a89