wayland/screencopy: avoid crash when capturing null screen

Prevent null pointer dereference in IccOutputSourceManager, WlrScreencopyManager, and ScreencopyManager when captureSource references a null screen.

changelog/next.md

@@ -4,3 +4,4 @@
 - Fixed Hyprland workspaces keeping their old id after Hyprland changes it.
 - Fixed desktop entries being parsed incorrectly with trailing whitespace or CRLF line endings.
 - Fixed `WlSessionLock.locked` changes not being emitted on unlock.
+- Fixed a crash when unplugging a screen being captured by ScreencopyView or trying to capture the fallback screen.

src/wayland/screencopy/image_copy_capture/image_copy_capture.cpp

@@ -220,6 +220,8 @@ IccOutputSourceManager* IccOutputSourceManager::instance() {
 }
 
 ScreencopyContext* IccOutputSourceManager::captureOutput(QScreen* screen, bool paintCursors) {
+	if (screen == nullptr) return nullptr;
+
 	auto* waylandScreen = dynamic_cast<QtWaylandClient::QWaylandScreen*>(screen->handle());
 	if (!waylandScreen) return nullptr;
 

src/wayland/screencopy/manager.cpp

@@ -25,6 +25,8 @@ namespace qs::wayland::screencopy {
 
 ScreencopyContext* ScreencopyManager::createContext(QObject* object, bool paintCursors) {
 	if (auto* screen = qobject_cast<QuickshellScreenInfo*>(object)) {
+		if (screen->screen == nullptr) return nullptr;
+
 #if SCREENCOPY_ICC
 		{
 			auto* manager = icc::IccOutputSourceManager::instance();

src/wayland/screencopy/wlr_screencopy/wlr_screencopy.cpp

@@ -34,6 +34,7 @@ WlrScreencopyManager* WlrScreencopyManager::instance() {
 
 ScreencopyContext*
 WlrScreencopyManager::captureOutput(QScreen* screen, bool paintCursors, QRect region) {
+	if (screen == nullptr) return nullptr;
 	if (!dynamic_cast<QtWaylandClient::QWaylandScreen*>(screen->handle())) return nullptr;
 	return new WlrScreencopyContext(this, screen, paintCursors, region);
 }