[automerger skipped] [RESTRICT AUTOMERGE] Fix UAF in clearkey service's MemoryFileSystem am: 9ba33b3586 -s ours am: 0a2abba43f -s ours am: a4e3bea9e4

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/av/+/13711823

Change-Id: Ic56cc6361b40290199fa024f3140ba7979cd675e