xwl: Include errors and warnings

(cherry picked from commit 439dcc4b)

xwl/clipboard.cpp

@@ -145,6 +145,8 @@ void Clipboard::doHandleXfixesNotify(xcb_xfixes_selection_notify_event_t *event)
 
     if (X11Source *source = x11Source()) {
         source->getTargets();
+    } else {
+        qCWarning(KWIN_XWL) << "Could not create a source from" << event << Qt::hex << (event ? event->owner : -1);
     }
 }
 
@@ -152,6 +154,7 @@ void Clipboard::x11OffersChanged(const QStringList &added, const QStringList &re
 {
     X11Source *source = x11Source();
     if (!source) {
+        qCWarning(KWIN_XWL) << "offers changed when not having an X11Source!?";
         return;
     }
 

xwl/selection_source.cpp

@@ -197,9 +197,11 @@ void X11Source::handleTargets()
                                                         );
     auto *reply = xcb_get_property_reply(xcbConn, cookie, nullptr);
     if (!reply) {
+        qCDebug(KWIN_XWL) << "Failed to get selection property";
         return;
     }
     if (reply->type != XCB_ATOM_ATOM) {
+        qCDebug(KWIN_XWL) << "Wrong reply type";
         free(reply);
         return;
     }