Fix a typo

At this point, desktop() is -1 since the client hasn't been moved to any
virtual desktop yet.

It seems like checking desktop() is a typo. It makes more sense to check
desktopId.

src/x11client.cpp

@@ -548,7 +548,7 @@ bool X11Client::manage(xcb_window_t w, bool isMapped)
             if (info->desktop()) {
                 desktopId = info->desktop(); // Window had the initial desktop property, force it
             }
-            if (desktop() == 0 && asn_valid && asn_data.desktop() != 0) {
+            if (desktopId == 0 && asn_valid && asn_data.desktop() != 0) {
                 desktopId = asn_data.desktop();
             }
             if (desktopId) {