Never generate $0.00 invoices
Summary: Ref T7769. It might possibly make sense to generate these some day, but for now they aren't payable and we have no use for them.
Test Plan:
- Generated $0.00 invoices, saw code decline to invoice.
- Generated a $7.99 invoice, got an invoice.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T7769
Differential Revision: https://secure.phabricator.com/D12878