Fix the low pixel size limit in Scale to New Size dialog

Summary:
This commit changes the limit for image size
in the dialog from 90k pixels to 100000k (100M) pixels
which is the same limit as in the File -> New dialog.

BUG:395267

Test Plan:
- trying to scale image to 1000M pixels in any dimension
(dialog should not allow for that)
- trying to scale image to 1000M pixels, but in a different
unit (according to dpi); dialog should not allow for that
- trying to scale image to 20k pixels, it works fine

Reviewers: #krita, woltherav

Reviewed By: #krita, woltherav

Subscribers: woltherav

Tags: #krita

Differential Revision: https://phabricator.kde.org/D19545