Fixed mUserId_shouldDeriveUidFromMainCaller test case fail

- getApplicationContext() return null in some test cases.
- Add null checking to avoid the NPE failed.

Fixes: 263542897
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.applications
Change-Id: I374b5bbf8911bd6d4eb992e0fa7b1a67c3d16a91
1 file changed