Disable scrolling while the context menu is showing.

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

@@ -1143,9 +1143,14 @@ public class ConversationListFragment extends MainFragment implements ActionMode
     new SignalContextMenu.Builder(view, list)
         .offsetX(ViewUtil.dpToPx(12))
         .offsetY(ViewUtil.dpToPx(12))
-        .onDismiss(() -> view.setSelected(false))
+        .onDismiss(() -> {
+          view.setSelected(false);
+          list.suppressLayout(false);
+        })
         .show(items);
 
+    list.suppressLayout(true);
+
     return true;
   }