CallFragment: fix the gray screen in rendezvous mode

GitLab: #1112

Change-Id: Iffa5c5bc10e6175117ea76a17d26e8426c500ad7

ring-android/app/src/main/java/cx/ring/fragments/CallFragment.kt

@@ -886,7 +886,8 @@ class CallFragment : BaseSupportFragment<CallPresenter, CallView>(), CallView,
 
     private fun generateParticipantOverlay(participantsInfo: List<ParticipantInfo>) {
         val overlayViewBinding = binding?.participantOverlayContainer ?: return
-        overlayViewBinding.participants = participantsInfo.filterNot {
+        binding?.previewContainer?.isVisible = participantsInfo.size > 1
+        overlayViewBinding.participants = if (participantsInfo.size == 1) participantsInfo else participantsInfo.filterNot {
             it.contact.contact.isUser && it.device == presenter.getDeviceId()
         }
         overlayViewBinding.init()