fcntl: Don't access nonexistent optional argument. Reported by Frank Busse <f.busse@imperial.ac.uk> in <https://lists.gnu.org/archive/html/bug-gnulib/2018-09/msg00018.html>. * lib/fcntl.c (rpl_fcntl): For actions that don't take an argument, don't consume an argument. For actions that take an 'int' argument, consume an 'int' argument.