Issue #10651: Fix "Remove all Guides" script bug

This patch attempts to resolve #10651 (closed).

Currently, trying to run the "Remove All Guides" script throws an error. This is because gimp-image-find-next-guide claims to accept 0 as an input parameter, but only accepts 1 or greater.

This patch fixes the range so that gimp-image-find-next-guide can accept 0 as intended. However, this may be a symptom of another larger issue - which is why I'm holding off on merging until @bootchk has a chance to look over it.