Add null checks for FABs in conversation list.

Fixes #12651.

app/src/main/java/org/thoughtcrime/securesms/conversationlist/ConversationListFragment.java

@@ -1145,16 +1145,24 @@ public class ConversationListFragment extends MainFragment implements ActionMode
   }
 
   private void fadeOutButtonsAndMegaphone(int fadeDuration) {
+    if (fab != null) {
       ViewUtil.fadeOut(fab, fadeDuration);
+    }
+    if (cameraFab != null) {
       ViewUtil.fadeOut(cameraFab, fadeDuration);
+    }
     if (megaphoneContainer.resolved()) {
       ViewUtil.fadeOut(megaphoneContainer.get(), fadeDuration);
     }
   }
 
   private void fadeInButtonsAndMegaphone(int fadeDuration) {
+    if (fab != null) {
       ViewUtil.fadeIn(fab, fadeDuration);
+    }
+    if (cameraFab != null) {
       ViewUtil.fadeIn(cameraFab, fadeDuration);
+    }
     if (megaphoneContainer.resolved()) {
       ViewUtil.fadeIn(megaphoneContainer.get(), fadeDuration);
     }