Dear Maintainer,

I noticed that icedove fails silently if one tries to save an e-mail (not
attachment!) using Ctrl+S, in cases where the resulting file name contains
characters like a colon which are not supported on the destination file
system.

This is often the case if you try to save a mail containing "Re:" in the
subject.

Steps to reproduce:
- Open any mail containing 'Re:' in the subject
- Press Ctrl+S
- Choose any VFAT formatted file system (e.g. USB drive) as destination
- Do not change the proposed file name
- Click save

Expected result:
- File is saved or icedove complains about invalid file name

Actual result:
- File is not saved, no message from icedove