[Translators] some typos in source

[Thomas Bellmann]

Maybe you can fix this (whitespace before "?") before string freeze: 

#: src/folderview.c:798 src/summaryview.c:4114
msgid "Do you really want to mark all mails in this folder as read ?"

#: src/plugins/att_remover/att_remover.c:418
msgid ""
"Do you really want to remove all attachments from the selected
messages ?\n"

#: src/plugins/vcalendar/vcalendar.c:1088
msgid ""
"You have no account matching any attendee.\n"
"Do you want to reply anyway ?"

Regards
Thomas