[6.1][FIX] Do not break on malformed messages.
fetchmail_attach_from_folder. backport improvements in exception handling on 10.0 to 6.1, to prevent exceptions in retireving one mail from breaking message retrieval for all other messages.
With the last commit, 1343e99, performance improved a lot as well, because messages that have already been retrieved are not parsed fully, which usually will be the bulk of messages.
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