flockc: segfaults when file name is not given

flockc: segfaults when file name is not given

$ flock -s
Segmentation fault

ltrace:
__libc_start_main(0x8048870, 2, 0xbfe9f404, 0x8049070, 0x8049060 <unfinished ...>
getopt_long(2, 0xbfe9f404, "+sexnouw:hV?", 0x80494e0, 0xbfe9f354) = 115
getopt_long(2, 0xbfe9f404, "+sexnouw:hV?", 0x80494e0, 0xbfe9f354) = -1
strtol(0, 0xbfe9f34c, 10, 0x80494e0, 0xbfe9f354 <unfinished ...>
--- SIGSEGV (Segmentation fault) ---
+++ killed by SIGSEGV +++

Addresses-Red-Had-Bugzilla: #489672
Signed-off-by: Karel Zak <kzak@redhat.com>