[wayland] Ensure Compositor is destroyed early enough

If startup fails and there is no Workspace the Compositor was destroyed
as a child of Application with the result of being destroyed after the
Wayland server resulting in a crash.

If the Workspace gets created the Compositor will be destroyed by the
Workspace, so there's no need to destroy it early.

main.cpp

@@ -423,6 +423,15 @@ void Application::destroyWorkspace()
     delete Workspace::self();
 }
 
+void Application::destroyCompositor()
+{
+    if (Workspace::self()) {
+        // compositor is destroyed together with Workspace
+        return;
+    }
+    delete Compositor::self();
+}
+
 void Application::updateX11Time(xcb_generic_event_t *event)
 {
     xcb_timestamp_t time = XCB_TIME_CURRENT_TIME;

main.h

@@ -166,6 +166,7 @@ protected:
     void createCompositor();
     void setupEventFilters();
     void destroyWorkspace();
+    void destroyCompositor();
     /**
      * Inheriting classes should use this method to set the X11 root window
      * before accessing any X11 specific code pathes.

main_wayland.cpp

@@ -73,6 +73,7 @@ ApplicationWayland::ApplicationWayland(int &argc, char **argv)
 
 ApplicationWayland::~ApplicationWayland()
 {
+    destroyCompositor();
     destroyWorkspace();
     if (x11Connection()) {
         Xcb::setInputFocus(XCB_INPUT_FOCUS_POINTER_ROOT);