xwayland: Allow for regular transport types for listen

Xwayland uses the command line option “-listen” to pass file descriptors
from the Wayland compositor.

That breaks the traditional, documented behavior of the “-listen”
command line option which is to enable a transport type.

Checks if the given option starts with a digit, otherwise treat it as a
regular transport type.

Closes: https://gitlab.freedesktop.org/xorg/xserver/issues/817
Suggested-by: Rodrigo Exterckötter Tjäder
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>

hw/xwayland/xwayland.c

@@ -115,6 +115,10 @@ ddxProcessArgument(int argc, char *argv[], int i)
     else if (strcmp(argv[i], "-listen") == 0) {
         CHECK_FOR_REQUIRED_ARGUMENTS(1);
 
+        /* Not an FD */
+        if (!isdigit(*argv[i + 1]))
+            return 0;
+
         NoListenAll = TRUE;
         if (listen_fd_count == ARRAY_SIZE(listen_fds))
             FatalError("Too many -listen arguments given, max is %zu\n",