Fix target adjusters sometimes not allowing abilities/cards to be used

[ssk97]

Currently, the spell or ability always checks the default target to check if it can be used. However, this fails if the target adjuster can adjust the targeting to be more lenient than

This isn't a perfect solution, as it allows cards to begin to be cast with no legal targets, but I can't think of a way to solve that. This fixes issues like [[Long River's Pull]]'s gift ability being unusable, as the card can only start being cast if there is a noncreature spell on the stack already.