Merge "Fix nullptr access when cow reader open fails" am: 9e6005ada4

Original change: https://android-review.googlesource.com/c/platform/system/core/+/2325397

Change-Id: Ic8cc95b0548039f6c04c24e6f4209a71c878c00a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>