genhash can throw a segmentation fault when not providing an argument

Before:
(gdb) run --server 127.1.0.1
Starting program: /usr/bin/genhash --server 127.1.0.1
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x0000000000406968 in inet_ston ()

after:
`genhash --port 80 --server=127.0.0.1`
MD5SUM = d41d8cd98f00b204e9800998ecf8427e