TV PiP: don't throw exception if entry restricted

Throwing exception when PiP entry is not allowed could crash existing
apps, instead simply log a helpful error message and don't go into PiP
silently.

Bug: 377961265
Test: use app that requests PiP entry in onPause and check logsi
Test: atest PinnedStackTests
Flag: android.app.enable_tv_implicit_enter_pip_restriction
Change-Id: I2b8d3802c7172f5d572e97d1a37dd40330ef6e37