Segfault sorting multiple files

[charles-randall]

Also probably the same as issue #7

Sorting multiple files also appears broken,

$ cat a.txt
a
$ cat b.txt
b
$ /tmp/msort a.txt
a
$ /tmp/msort b.txt
b
$ /tmp/msort a.txt b.txt 
Segmentation fault (core dumped)

Can you reproduce this?