Check mChooserListAdapter for null when using App Predictor Service

mChooserListAdapter will be null if there are no apps that can perfrom
the action (Share, Open With).

Bug:127305716
Test: Flashed and got the appropriate behavior: https://screenshot.googleplex.com/VcJFGHadspN
Change-Id: I5ca647cd974a02041522409fc070c27df2bdc9c4