main: set isShuttingDown after display dispatch reaches the end

relates to #3558

src/main.cpp

@@ -104,6 +104,8 @@ int main(int argc, char** argv) {
     // If all's good to go, start.
     g_pCompositor->startCompositor();
 
+    g_pCompositor->m_bIsShuttingDown = true;
+
     // If we are here it means we got yote.
     Debug::log(LOG, "Hyprland reached the end.");
     g_pCompositor.reset();