Helpers: resetActivePageHeight() ignores fixed toolbars

Any external fixed toolbar widget with option updatePagePadding set to true
need not be accounted for when calculating page height, because it updates the
page padding to account for itself.

(cherry picked from commit 2060bca3ce7ec8aa642eca5da59a8effd950d776)

Closes gh-7802
Fixes gh-7739