validate concurrency parameter

[codekitchen]

I recently ran into a bug in fast-glob where it was setting concurrency: 0 in some environments. This triggers a nasty situation where all work is just queued up forever and fastq silently never makes progress.

It might be good to validate the concurrency parameter and not allow a value less than 1.

[mcollina]

Good spot! Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[KyleAMathews]

This should be closed