dojox/mobile/scrollable ignores constraint == false when content is smaller than container

[Eric Durocher]

When the content is smaller than the scrollable, the value of "constraint" is ignored - thus, the scrollable always returns to the "zero" point when scrolled.

Can be reproduced by modifying dojox/mobile/tests/test_ScrollableView-demo.html, adding

 data-dojo-props="constraint:false"

on the first ScrollableView. Run this in a desktop browser. When the window is smaller than the list, scroll is not constrained, whereas if the window if higher than the list, it bounces back to the top, which is not consistent.

[Eric Durocher]

In [31246]:

fixes #17028. Take the constraint attribute into account when content is smaller than viewport. Patch by Nick Maynard (IBM, CCLA). !strict