Hopefully the "right" fix for the zip crash

Earlier,

```
✗ ../run/john -fo:pkzip zip-crasher
Error, length of full data does not match the salt len. $pkzip$1*1*2*0*0*0*0*0*0*0*1*0000*00*$/pkzip$
[1]    13639 segmentation fault (core dumped)  ../run/john -fo:pkzip zip-crasher
```

Now,

```
✗ ../run/john -fo:pkzip zip-crasher
No password hashes loaded (see FAQ)
```

zip-crasher,

```
✗ cat zip-crasher
$pkzip$1*1*2*0*0*0*0*0*0*0*1*0000*00*$/pkzip$
```