Don't throw exception on unexpected BT device addition.

Fix for reported bug where settings app crashes while trying to share
a picture. Bug report showed IllegalStateException thrown with message
"Got onDeviceAdded, but cachedDevice already exists." Changed code to
print an error message to the log and ignore the unexpected event,
rather than throwing an uncaught exception that crashes the app.

Bug: 2192884
Change-Id: I016be6a1616b317b2289768d18ae9f069a49445e