vold: do not set gc sleep time with zero dirty segments am: 0b5f397e2b am: f605ac329b am: 529d797f58

Original change: https://android-review.googlesource.com/c/platform/system/vold/+/2033123

Change-Id: I04825446e3a9c4b65d66ec345bfa6d5a4d3b3aca
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>