Missing icon in scheduled emails

The scheduled emails in drafts do not show the image of the clock next to the object (see attached "Image 1").

The same image is instead regularly shown by opening the email (see attached "Image 2").

Analyzing the source code we note that the problem lies in the extension of the image file:
> when NOT shown the file name is this:

resources/com.sonicle.webtop.mail/5.5.6/laf/default/statusscheduled_16.svg

> when the file name is shown this is:

resources/com.sonicle.webtop.mail/5.5.6/laf/default/statusscheduled_16.png

Internal Ref: #62358 - Thanks to Federico Ballarini