x11/panelwindow: avoid using destroyed panel stack after free

changelog/next.md

@@ -19,3 +19,4 @@
 - Fixed crashes when failing to create a `ScreencopyView`.
 - Fixed `PwNodePeakMonitor` crashing when sampling a stream with mismatched channels from the node.
 - Fixed unsetting `PopupAnchor.item` causing a crash.
+- Fixed hiding the last `PanelWindow` on screen causing a crash under X11.

src/x11/panel_window.cpp

@@ -57,7 +57,7 @@ public:
 			}
 
 			// from the bottom up, update all panels
-			for (auto* panel: panels) {
+			for (auto* panel: this->mPanels[panel->engineGeneration]) {
 				panel->updateDimensions();
 			}
 		}