os-support: systemd-logind: don't hard-crash Xserver on strdup() fail

No need to directly hard-crash the Xserver when strdup() fails, instead
try to handle the situation gracefully.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

hw/xfree86/os-support/linux/systemd-logind.c

@@ -492,7 +492,11 @@ connect_hook(DBusConnection *connection, void *data)
                    error.message);
         goto cleanup;
     }
-    session = XNFstrdup(session);
+    session = strdup(session);
+    if (!session) {
+        LogMessage(X_ERROR, "systemd-logind: out of memory\n");
+        goto cleanup;
+    }
 
     dbus_message_unref(reply);
     reply = NULL;