Do not crash on wayland, gracefully exit with error instead

Summary:
Sadly, XTestQueryExtension just segfaults under wayland.
Avoid it by detecting QPA used.

BUG: 406599

Test Plan:
Nice error message when running in Wayland session.
{F6833467}

Still works in X11
{F6833069}

Reviewers: aacid, kossebau, jgrulich, #kde_applications, pino, ngraham

Reviewed By: pino

Subscribers: pino, ngraham

Tags: #kde_applications

Differential Revision: https://phabricator.kde.org/D21267

krfb/main.cpp

@@ -121,13 +121,21 @@ int main(int argc, char *argv[])
 
     app.setQuitOnLastWindowClosed(false);
 
-    if (!checkX11Capabilities()) {
+    if (QX11Info::isPlatformX11()) {
+        if (!checkX11Capabilities()) {
+            return 1;
+        }
+
+        // upgrade the configuration
+        checkOldX11PluginConfig();
+    } else {
+        KMessageBox::error(nullptr,
+                           i18n("Desktop Sharing is not running under an X11 Server. "
+                                "Other display servers are currently not supported."),
+                           i18n("Desktop Sharing Error"));
         return 1;
     }
 
-    // upgrade the configuration
-    checkOldX11PluginConfig();
-
     //init the core
     InvitationsRfbServer::init();