[PATCH cygport] lib/src_prep.cygpart: Fix incorrect options passed to unzstd in unpack()

[Jon Turney]

On 04/08/2023 19:39, Yasutaka ATARASHI via Cygwin-apps wrote:
> ASSI via Cygwin-apps writes:
>> That's true for bunzip2 and gunzip, but not for zstd (where the output
>> file can be independently specified).
> 
> Ah ha. The attached patch recovers to use the `-o` option for `unzstd`.

Thanks. I applied this.

I added '-f' as that seems to be needed to ensure 'cygport prep' works 
when run a second time.