Content is overlapping panels area when adding high resolution images

Steps to reproduce:

1. Resize you screen
2. Open a page in Wiki mode
3. Add an image (with a higher resolution, e.g. 1440x990 px) to that page by clicking on the "Attached image" button
4. Save the page

Actual behaviour:

1. The image is overlapping with panels.

Expected behaviour:

1. The image is fitting with the editor's space.