Fixed warning when compiling with -Wshorten-64-to-32 flag

Compiling commander with the `-Wshorten-64-to-32` or `-Wconversion` flag generates the following warning:

```
warning: implicit conversion loses integer precision: 'unsigned long' to 'int'
```

Changing the type from `int` to `size_t` fixes it.

PS: Sorry for the whitespace changes. Silly Sublime Text 2!