[pm] fix NPE in PreferredComponent

The list of ResolveInfo is from a previous snapshot, so it's possible
that by the time the code reaches PreferredComponent.isSameSet, some of
the apps in the list has already been uninstalled. This CL adds an NPE
fix. A longer term fix should pass the same snapshot into
PreferredComponent to ensure consistency.

BUG: 320033788
Test: presubmit

Change-Id: I488943043a85be23558c06e020f4a91544fe3dc5