Fix ongoing autogenerated summaries

Fixes an issue where the autogroup summary wasn't being
marked with the ongoing flag if the ongoing notifications
were posted before the summary was created and then never updated

Test: GroupHelperTest, manually look at "android" group when two
system USB notifications are shown
Bug: 225393724

Change-Id: Id7953bafa4f709bb053f24b72be3925465931ec5
4 files changed