Always return null when accessing provider unavailable to instant app

When the provider is not cached we first try to resolve it which would
fail and return null. When the provider is cached we would return a
SecurityException.

This unifies the behavior for instant apps.

Fixes: 92984448
Test: cts-instant-tradefed run commandAndExit cts-instant-dev
      -m CtsPermissionTestCases
      --test=android.permission.cts.ProviderPermissionTest

Change-Id: I00120f597bd10ac02232bcc2b25dd0d6c4342bf2