Fix an assumption that UserHandle.myUserId() always returns the main

user.

In some cases, e.g. in Private Space Storage Info fragment it returns
the Private profile id and this was leading to a crash, see b/378471943.

Bug: 378471943
Test: Manually and presubmit
Flag: com.android.settings.flags.utils_return_user_handle_for_current_user_id
Change-Id: I5f7bedc66ebcac8b0ae265b7189dd1821edb3cd7