libprocessgroup: fix reset of file_v2_name am: 72254810

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/24271775



Change-Id: I36800e066ce74f7b84161451a01a37da08f9e002
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>