You cannot legitimately be aware of the sellers intentions with the proceeds of the sale prior to a purchase. Whether your baker is selling crack cocaine on the side, or Orson is a bigoted gay-bashing asshole who supports anti-gay parades, it should be divorced from content. Otherwise, normatively, we are placing an insurmountable burden on ourselves of ascertaining people's intentions and morality prior to any commercial transaction.
Question is, once you know their intentions, should you re-evaluate the purchase. And the answer is, obviously yes! If you're talking about economic sanctions, and that's what a boycott is, it needs to be directed against the core of this bigotry. If you legitimately believe that your contribution to Card via the movie is primarily going to lead to increased anti-gay activity, and that is reprehensible enough to you, then screw it. However if you think that out of your ticket cost, the tiny portion that goes to Card, and the tinier portion that goes towards his activism, is a worthwhile price to pay for the pleasure of watching the movie adaptation of a truly awesome book, the answer is less clear cut.
Therefore, my position: YMMV. I personally will watch the movie - because the short sum that goes from my ticket to Card is easily offset. Doesn't work from a categorical imperative perspective, but as I often say, fuck Kant!