[BUG] 2nd time halving with DM shows "halve time" instead of "complete"

[Geda173]

Describe the bug
When spending DM to halve the time of a building, the button still displays "halve time" afterwards. After halving the time, it should read "Complete" instead.

[tiweb442]

Fix submitted in #1496 — mirrors shipyard DM halve/complete behavior for building queues.

Validated on production (https://space.tiweb-host.com): after halving once, the sidebar shows Complete instead of Halve again.