lei: bail out earlier on IMAP writer failures
Excessive IMAP connections can overload IMAP servers and cause
clients to be disconnected without diagnostic messages.
Use $lei->fail on these exceptions to propagate errors to the
CLI ASAP to avoid further errors down the line.
This ought to make problems more apparent for users using IMAP
destinations.
Reported-by: Ricardo Ribalda <ribalda@chromium.org>
Link: https://public-inbox.org/meta/CANiDSCsDfutAUMBLPZbxdyka+_jnhv+4YNYdL9QPRoC=wNUGCQ@mail.gmail.com/