par2create crashes when input filename is only one character.

[will-ca]

$ echo 'Some Data.' > D
$ par2create D

Block size: 4
Source file count: 1
Source block count: 3
Recovery block count: 1
Recovery file count: 1

Opening: D
terminate called without an active exception
Aborted (core dumped)

$ ls
D


$ echo 'Some Data.' > D2
$ par2create D2

Block size: 4
Source file count: 1
Source block count: 3
Recovery block count: 1
Recovery file count: 1

Opening: D2
Computing Reed Solomon matrix.
Constructing: done.
Wrote 4 bytes to diskets
Writing recovery packets
Writing verification packets
Done

$ ls
D  D2  D2.par2  D2.vol0+1.par2

Well, that's a bit silly.

[animetosho]

See #149 and #165