Shrinking width of browser horizontally may let grid disappear giving all space to message view

If the browser window in which I opened webtop is narrowed sideways, for example to place two different windows side by side, if you have the preview on the right, the mail column is compressed and disappears in some conditions

Steps to reproduce:

• access the mail service and set the preview on the right
• widen the mail folders column to the right
• decrease the horizontal size of the browser window to half the screen

Expected behaviour:

• the three columns (folders, mail and preview) are resized and all remain visible

Actual behaviour:

• the central column of the mails is "crushed" by the two side columns and disappears from view (see attached image)

Thanks to Andrea Marchionni