Phantom image size increase on slow window resize

[khaykov]

This issue got uncovered after #835 got merged.

When you slowly resize window sometimes image bounding box gets too large, which results in this (all the space at the bottom is the image box)

To test, slowly resize the window.

[daniloercoli]

Re-opening this issue, since the proposed fix in #838 does break the editor on mobile devices, and was reverted here :https://github.com/wordpress-mobile/AztecEditor-Android/pull/855