Validate checkpoints in checkpoint_change()

[altoiddealer]

I believe this solves #2089

EDITED comment below in bold text

Upon reviewing the relevant code in this issue, I can see that the option hr_checkpoint_name was not **100% flawlessly ** validating the checkpoint before applying checkpoint_change(). in processing module line 1272 I believe that get_closet_checkpoint_match() may possibly return an invalid value?

First pass sd_checkpoint_model checkpoints were being validated outside checkpoint_change().

Rather than creating another duplicate validation step specifically for hr_checkpoint_name outside the function, simply validate all checkpoints within checkpoint_change()

[altoiddealer]

A part of me wants to mark this as "Draft", because I'm starting to think this does not solve #2089

I'm leaving this open as I think it is still a good idea to validate all requested checkpoint changes in this function