Fix android.os.strictmode.LeakedClosableViolation

Ensure the file opened in
  com.android.server.PersistentDataBlockService.getBlockOutputChannel
is consistently closed as required.

Test: atest PersistentDataBlockServiceTest
Bug: 296945440
Change-Id: I6b6cee1d6477c4c615733154efa9ad6af5fc96cc
1 file changed