Fix crash in TranserPipe.

Sometimes the pipe has been closed when it's thread tries to access

E AndroidRuntime: *** FATAL EXCEPTION IN SYSTEM PROCESS: TransferPipe
E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.FileDescriptor android.os.ParcelFileDescriptor.getFileDescriptor()' on a null object reference
E AndroidRuntime: 	at com.android.internal.os.TransferPipe.run(TransferPipe.java:184)
E AndroidRuntime: 	at java.lang.Thread.run(Thread.java:818)

Change-Id: I0fcd4a3334b49972903f2cb0edb51323ba3f49e5