CLI pmtiles extract does not accept absolute paths for output

[GaborFarkas]

Hello, thanks for the great tool! I could set up an extraction pipeline pretty effortlessly with pmtiles extract apart from a minor issue.

I created the pipeline with Docker from the start (protomaps/go-pmtiles:latest) and thus debugging was a bit limited, but it turned out that if I pass an absolute path as the output, the tool fails right after fetching the required tiles with the following trace:

2.972 fetching 11 dirs, 11 chunks, 8 requests
10.79 Region tiles 514, result tile entries 514
10.79 fetching 514 tiles, 62 chunks, 36 requests
10.79 2025/03/06 11:48:51 main.go:179: Failed to extract, invalid argument

It goes away when I cd into the output folder and use a relative path. Not a large issue, but can be a head scratcher for people experimenting with pmtiles especially in a containerized environment.

Might affect other paths, I did not have time to test e.g. input.