Fix for Mark All Emails As Read

[macejiko]

Problem was same as for Delete All Mails from here #1 : We call function for empty list of emails.
I've added separate function for emails retrieving

@lasselindqvist I've checked it for my gmail account. It works well. Haven't checked for anything else.

[lasselindqvist]

Thanks. Seems like this was undetected because the method would mostly work if some other method was called before it populating the mail list.
I'll try to release this during the weekend.