Camera: Handle abandoned output surface in encodeSessionConfiguration

The GraphicBufferProducer contained in the surface in
SessionConfiguration may become null. Check against that
to avoid NPE.

Flag: EXEMPT bugfix
Test: `atest -c -d ZoomCaptureTest --iteration=10` on cuttlefish
Bug: 351035860
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5df04fca1d97be2e3a8eb665af5ca346c8c552b4)
Merged-In: I9563c39fe6cd59b12f16ad6cb0cafb487c1b0d28
Change-Id: I9563c39fe6cd59b12f16ad6cb0cafb487c1b0d28