games/sulis: Fix area elevation in act3 areas

Backported patch [0] for upstream issue #220 [1], which blocks
act3 campaign (fix area elevation in act3 areas).

[0] https://github.com/Grokmoo/sulis/commit/af773b9f09753ea8614ac82dd8033c870a5a779c?diff=unified&w=0
[1] https://github.com/Grokmoo/sulis/issues/220

PR: 283358