TWP: Staircase in Edmund's mansion disrupts scrolling

[tag2015]

After removing the "out of order" sign and climbing the staircase, the screen no longer scrolls horizontally.
This prevents access to section 3.1 (where you need the MMucasflem manual) and, even more importantly, you can't leave the room anymore.

Note: you can workaround the issue skipping the animation with ESC

[scemino]

In 979207a3:

TWP: Fix cutscene regressions

Fix #15574, #15576 and #15577