Use `start_enabled` attribute for triggers

[thokkat]

Of the two triggers that open the gate to get to the 4 rooms with switch riddles in Irdorath only one is enabled. Both are activated at the same time and their enable status is toggled afterwards.

Setting both to enabled on first load lead to the bug that both gate up and down animations were played on first activation but none on second. This change fixes those cases. https://github.com/Try/OpenGothic/commit/20af3701522cf0141f37e8f6d1a707d0b06dc48e had a fix for first case but second one was still open.

Also added a missing clear command reported by static analyzer for deferred triggers.