If a message date would fail to parse, the worker would never receive
the MessageInfo it asked for, and so it wouldn't display the message.
The problem is the spec for date formats is too lax, so trying to ensure
we can parse every weird date format out there is not a strategy we want
to pursue. On the other hand, preventing the user from reading and
working with a message due to the error format is also not a solution.
The maildir and notmuch workers will now fallback to the internal date, which
is based on the received header if we can't parse the format of the Date header.
The UI will also fallback to the received header whenever the date header can't
be parsed.
This patch is based on the work done by Lyudmil Angelov <lyudmilangelov@gmail.com>
But tries to handle a parsing error a bit more gracefully instead of just returning
the zero date.
Aerc usually used the path []int{1} if it didn't know what the proper path is.
However this only works for multipart messages and breaks if it isn't one.
This patch removes all the hard coding and extracts the necessary helpers to lib.
When message dates failed to parse, the error displayed would try to
include the time object it failed to obtain, which would display as
something like 0001-01-01 00:00:00 UTC, which isn't of much help.
Instead, display the text we were trying to parse into a date, which
makes the problem easier to debug.
Things like FetchEntityPartReader etc can be reused by most workers
working with raw email files from disk (or any reader for that matter).
This patch extract that common functionality in a separate package.
