FL-1507 Keep zero-quantity price adjustment lines

Jira: https://freedomgroupinternational.atlassian.net/browse/FL-1507. mapTickets dropped every item with quantity 0, but Lightspeed K sends partial voids and price adjustments as priced quantity-0 lines (real check: Chilean Sea Bass price -270.42 quantity 0). Without them the item prices no longer add up to the ticket total, which inflates BestSellers item revenue in AMS. Now only empty lines (quantity 0 and price 0) are skipped. Ticket totals and dashboard revenue are unchanged. Test built from the real check. After merge: tag v1.9.4 and bump etl !42. 🤖 Generated with Claude Code

Closes FL-1507