Fix modal scrolling for overflow

[lulalala]

When modal contains absolute positioned element which is taller than available screen, the modal scrolling is not triggered. By using scrollHeight the extended height is taken into account.

scrollHeight is how Bootstrap modal determines whether to trigger scrolling.

The bug demo:
https://jsfiddle.net/lulalala/ngjvzwkc/1/

[jlukic]

The fix above doesnt work for a few reasons

• When sizes are calculated the modal has display: none;
• Height calculation is used for vertical centering, and offscreen calculation is based on relative position of modal centering
• Modifying modal height to use scrollHeight would change the centering

7450aa3 adds a new loading state for calculating height, and uses both heights together. If scrollHeight is larger than modal base height, it'll use scrollHeight to calculate whether the modal is off stage.

[lulalala]

thanks for the fix!