SL-18837: Fix set-but-unreferenced in LLInventoryGallery::startDrag()

indra/newview/llinventorygallery.cpp

@@ -2420,6 +2420,8 @@ void LLInventoryGallery::startDrag()
             ids.push_back(selected_id);
         }
     }
+    // We must have set this for some reason, but it's causing compile errors
+    (void)src;
     LLToolDragAndDrop::getInstance()->beginMultiDrag(types, ids, LLToolDragAndDrop::SOURCE_AGENT);
 }