Go back to using ascii-ized filenames for Amazon

Apparently, their email service has stopped reading metadata
from file contents. Hurray!

src/calibre/gui2/email.py

@@ -165,6 +165,11 @@ def send_mails(jobnames, callback, attachments, to_s, subjects,
             # irony that they are called "tech" companies.
             # https://bugs.launchpad.net/calibre/+bug/1989282
             from calibre.utils.short_uuid import uuid4
+            if '@kindle.com' in to:
+                # https://www.mobileread.com/forums/showthread.php?t=349290
+                from calibre.utils.filenames import ascii_filename
+                aname = ascii_filename(aname)
+            else:
                 aname = f'{uuid4()}.' + aname.rpartition('.')[-1]
             subject = uuid4()
             text = uuid4()