x11/panelwindow: do not look up engine generation in ~XPanelWindow()

Looking up engine generation in the destructor causes occasional
crashes. This commit caches it to prevent that from happening.

Author: outfoxxed

src/x11/panel_window.cpp

@@ -40,17 +40,20 @@ class XPanelStack {
 	}
 
 	void addPanel(XPanelWindow* panel) {
-		auto& panels = this->mPanels[EngineGeneration::findObjectGeneration(panel)];
+		panel->engineGeneration = EngineGeneration::findObjectGeneration(panel);
+		auto& panels = this->mPanels[panel->engineGeneration];
 		if (!panels.contains(panel)) {
 			panels.push_back(panel);
 		}
 	}
 
 	void removePanel(XPanelWindow* panel) {
-		auto& panels = this->mPanels[EngineGeneration::findObjectGeneration(panel)];
+		if (!panel->engineGeneration) return;
+
+		auto& panels = this->mPanels[panel->engineGeneration];
 		if (panels.removeOne(panel)) {
 			if (panels.isEmpty()) {
-				this->mPanels.erase(EngineGeneration::findObjectGeneration(panel));
+				this->mPanels.erase(panel->engineGeneration);
 			}
 
 			// from the bottom up, update all panels
@@ -61,7 +64,8 @@ class XPanelStack {
 	}
 
 	void updateLowerDimensions(XPanelWindow* exclude) {
-		auto& panels = this->mPanels[EngineGeneration::findObjectGeneration(exclude)];
+		if (!exclude->engineGeneration) return;
+		auto& panels = this->mPanels[exclude->engineGeneration];
 
 		// update all panels lower than the one we start from
 		auto found = false;

src/x11/panel_window.hpp

@@ -98,6 +98,7 @@ private slots:
 	Margins mMargins;
 	qint32 mExclusiveZone = 0;
 	ExclusionMode::Enum mExclusionMode = ExclusionMode::Auto;
+	EngineGeneration* knownGeneration = nullptr;
 
 	QRect lastScreenVirtualGeometry;
 	XPanelEventFilter eventFilter;