Skip using the AppPredictionService if the component is not available

This CL adds a safeguard in ShareSheet to avoid calls to
AppPredictionService when the service is defined but is not available,
for example in the case of a wrong AiAi apk pushed from GooglePlay.

Bug: 138595943
Test: Manual test by removing the AiAi package from device

Change-Id: I4109c5122faa753d5111ee45698301cb6ccdd7b5