Fix interaction between sentence templates and dice entropy

[philipmw]

In phrase.shop v1, you'd first build a phrase from parts (which requires no entropy), then generate it (which does). With dice entropy, the app would let you build the phrase but keep the Generate button disabled until you roll the dice enough times. This ensured we don't try to generate the phrase until we have enough entropy.

In v2, building and generating are combined into one step, but the entropy check now happens at the wrong time and for the wrong amount.