[wayland] Ensure KWin::atoms are destroyed before doing xcb_disconnect

Destroying the Atoms might call into xcb as a request might have to be
discarded. If atoms are destroyed after disconnecting xcb, this'll crash.

main.cpp

@@ -200,7 +200,13 @@ void Application::start()
 Application::~Application()
 {
     delete options;
+    destroyAtoms();
+}
+
+void Application::destroyAtoms()
+{
     delete atoms;
+    atoms = nullptr;
 }
 
 void Application::crashChecking()

main.h

@@ -181,6 +181,7 @@ protected:
         m_connection = c;
         emit x11ConnectionChanged();
     }
+    void destroyAtoms();
 
     bool notify(QObject* o, QEvent* e);
     static void crashHandler(int signal);

main_wayland.cpp

@@ -76,6 +76,7 @@ ApplicationWayland::~ApplicationWayland()
     destroyWorkspace();
     if (x11Connection()) {
         Xcb::setInputFocus(XCB_INPUT_FOCUS_POINTER_ROOT);
+        destroyAtoms();
         xcb_disconnect(x11Connection());
     }
     if (m_xwaylandProcess) {