Problems with caption alignment in HTML when long descriptions present

[sean-fitzpatrick]

I am seeing some incorrect placement of captions in a sidebyside when a long description is present.
So far I've only noticed it in the case of a subfigure with an empty caption.

Examples:
https://opentext.uleth.ca/Math1410/sec_space_coord.html#fig_coordplanes
https://opentext.uleth.ca/apex-calculus/sec_shell_method.html#fig_shell_intro
https://opentext.uleth.ca/apex-calculus/sec_disk.html#fig_washeridea1

But in other cases it's just fine, like here:
https://opentext.uleth.ca/apex-calculus/sec_ABC.html#fig_abcintro

I think the problem is occurring when the following two conditions are satisfied:

1. The images are generated with Asymptote
2. All the images in the sidebyside are the same size

Maybe it is because we are stacking three things in this case:

• the "link to full size image" used for Asymptote figures
• the info button for the long description
• the caption

[rbeezer]

Should be closed by #2774.