fix FileNotFound exception when attempting to read bubble xml

BubbleDataRepository tried to read the xml file before a write,
and the xml file is only created on write if it didn't exist,
which caused the FileNotFound exception.

Bug: 158231089
Test: BubblePersistentRepositoryTest
Change-Id: I7cd75b1d74be277df49f433338ad814ce50c87c1
2 files changed