Don't stop MediaProjection sessions without display

When device lock would otherwise stop MediaProjection.

Bug: 370108833
Test: atest MediaProjectionManagerServiceTest
Flag: android.companion.virtualdevice.flags.media_projection_keyguard_restrictions
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:21b5c2f81085826dba071f98bbe0068cd9839289)
Merged-In: Ic5179113180d3bb71d813aeed02ae2a302190965
Change-Id: Ic5179113180d3bb71d813aeed02ae2a302190965