(emacs) Full-width characters break tree-style display

[Leo Gaspard]

When on tree-style display, any mail whose From: includes full-width
characters will see its tree-style display broken: notmuch mode
apparently assumes that each character is half-width.

For example, japanese characters are not: you can test it by sending
mail from 差出人 or similar characters.

Well, this is the last of the issues I've had until now. Anyway, this
won't make me budge: notmuch + emacs notmuch-mode is wayyyy better than
everything else I tried, despite these minor annoyances!

So thank you for notmuch, and cheers :)
Leo