Fix rendering issue when deleting the last message in a conversation.

app/src/main/java/org/thoughtcrime/securesms/conversation/ConversationFragment.java

@@ -250,8 +250,11 @@ public class ConversationFragment extends LoggingFragment {
     this.messageCountsViewModel = ViewModelProviders.of(requireActivity()).get(MessageCountsViewModel.class);
     this.conversationViewModel  = ViewModelProviders.of(requireActivity(), new ConversationViewModel.Factory()).get(ConversationViewModel.class);
 
-    conversationViewModel.getMessages().observe(this, list -> {
+    conversationViewModel.getMessages().observe(this, messages -> {
-      getListAdapter().submitList(list);
+      ConversationAdapter adapter = getListAdapter();
+      if (adapter != null) {
+        getListAdapter().submitList(messages);
+      }
     });
 
     conversationViewModel.getConversationMetadata().observe(this, this::presentConversationMetadata);

paging/lib/src/main/java/org/signal/paging/FixedSizePagingController.java

@@ -6,6 +6,7 @@ import androidx.lifecycle.MutableLiveData;
 import org.signal.core.util.concurrent.SignalExecutors;
 import org.signal.core.util.logging.Log;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.Executor;
 
@@ -57,6 +58,11 @@ class FixedSizePagingController<E> implements PagingController {
       return;
     }
 
+    if (loadState.size() == 0) {
+      liveData.postValue(Collections.emptyList());
+      return;
+    }
+
     int leftPageBoundary  = (aroundIndex / config.pageSize()) * config.pageSize();
     int rightPageBoundary = leftPageBoundary + config.pageSize();
     int buffer            = config.bufferPages() * config.pageSize();