Fix for succession law glitch

Just to clarify: It looks like adding `allow = {}` blocks to succession laws causes the game to only apply the succession related opinion modifiers to characters who meet the requirements inside that allow. And it looks like it also mixes up scopes when it does so, since adding `is_ruler = no` shouldn't work in what should be a title scope, but it clearly does. Note that I tested this fix fairly thoroughly, but it's possible it isn't going to cover every case; anyone playing should keep a weather eye out for those modifiers just in case.