Persistent Patches fix - unpatch prior to patching if needed

[kyleengan]

Steps to reproduce bug this PR is (theoretically) fixing (issue link: #117):

1. Start Forge Classic with --persistent-patches feature flag turned on
2. Load a model, add a prompt containing usage of at least one Lora
3. Set a non-random Seed for easier observation
4. Hit "Generate"
5. Significantly alter a Lora weight in the prompt (this makes it easier to check for changes to the image)
6. Hit "Generate"
7. [BUG] Observe the utter lack of change in the image
8. PRESUMED CAUSE: the persistent patches feature (correctly) prevented an unpatch after the first Generate, so the updated Lora weights aren't correctly patched in
9. Hit "Generate" again (no changes to prompt/loras!)
10. Observe the image change correctly according to the Lora weight alteration in step 5.

Persistent Patches is pretty much THE reason I switched to using Forge Classic, but I noticed that I had to hit Generate an extra time each time I fiddled with Lora weights. This bugged me enough to submit a PR with a proposed fix.

Thanks!

NOTE: I'm not a Python dev at all, so please let me know if any changes are preferred to the proposed implementation (or, if you don't wanna wait on me, I won't be offended if you fix the PR up how you like prior to inclusion, assuming you want to merge this :) )