Codefix: check the result of dynamic_cast for nullptr

src/toolbar_gui.cpp

@@ -1441,7 +1441,9 @@ public:
 			NWidgetBase *nwid = it->get();
 			nwid->current_x = 0; /* Hide widget, it will be revealed in the next step. */
 			if (nwid->type == NWID_SPACER) continue;
-			lookup[dynamic_cast<NWidgetCore *>(nwid)->GetIndex()] = std::distance(this->children.begin(), it);
+			NWidgetCore *nwc = dynamic_cast<NWidgetCore *>(nwid);
+			assert(nwc != nullptr);
+			lookup[nwc->GetIndex()] = std::distance(this->children.begin(), it);
 		}
 
 		/* Now assign the widgets to their rightful place */