Check if the display is attached when updating config

The display might not be added yet or be already detached when
config is updated.

Bug: 32983305
Test: android.media.cts.EncodeVirtualDisplayWithCompositionTest
Test: #testVirtualDisplayRecycles
Change-Id: I3b0e52e8ebb93a57ab6b0e80c0599db33ce2ae03