Fix toggling optional rule groups

[jasonpanosso]

fix a regression introduced in deepnight/ldtk@225a891faae5b7d6b5b9a067460a8202e1e17d4b

I simply swapped conditional branches, and built/tested via npm run pack-linux-x86 and it seems to have fixed the regression

closes #1059

also, apologies if this should be merged into master, not completely sure on the repository setup/regular practices.

P.S. Thanks so much for the awesome tool!! :)

[imranmollajoy]

Hello. Will this be merged? Optional rules are very useful. Currently its cumbersome to open the ldtk as text file to toggle the isOptional value.