Merge branch 'missing_assert' into 'master'

Add missing assertion

See merge request OpenMW/openmw!3751

components/lua_ui/element.cpp

@@ -280,6 +280,7 @@ namespace LuaUi
                 auto children = parent->children();
                 auto it = std::find(children.begin(), children.end(), mRoot);
                 mRoot = createWidget(layout(), 0);
+                assert(it != children.end());
                 *it = mRoot;
                 parent->setChildren(children);
                 mRoot->updateCoord();