Prune policy can't be set to 0%

[adamhl8]

If Max Unused After Prune is set to 0, it doesn't actually save at 0 and instead is reset to 10%.

[garethgeorge]

Thanks for reporting this. Just want to call out that it's typically not a good idea to set max unused after prune to 0% as restic will very aggressively repack blobs. You might look at setting it to a very low percentage e.g. 2-5%.

But this bug definitely is something that needs fixing -- the form should accept the value none the less. I've started looking at an overhaul of my form implementation in #592 where I'd like to clean up this problem along with a class of related bugs.