fix -o

-o didn't actually redirect output to that file, it just created it and left it empty, still writing to stdout. This patch fixes that.

before:
```shell
$ cat foo
hello world!
$ spp -o bar foo
hello world!
$ cat bar
$ 
```
after:
```shell
$ cat foo
hello world!
$ spp -o bar foo
$ cat bar
hello world!
$ 
```