Image toolbar positioning with multiple editors

[afercia]

When multiple editors are used on a post/page edit screen, the image toolbar position calculation may get confused:

Just add some text or even just blank space before the image in the second editor and things get better:

[helen]

Possibly related: #22785 (I had closed it because I hadn't seen it in a while, but was the same problem).

[azaozz]

In 31235:

TinyMCE: fix vertical positioning of the image toolbar when there are several instances of the editor. Props avryl, fixes #31028.

[iseulde]

#31366 was marked as a duplicate.