bug#16145: ERC disregards data to be logged when reconnecting

[Ivan Shmakov <ivan@siamics.net>]

	Upon reconnecting to the server, erc-connect-pre-hook is run,
	which, by default, results in erc-initialize-log-marker being
	called, and the erc-last-saved-position marker reinitialized.

	The problem is that no calls to erc-save-buffer-in-logs are made
	when the connection is closed, resulting in the entire previous
	ERC session silently disregarded, and never saved in the logs.

	Presuming that erc-initialize-log-marker was really meant to
	only initialize erc-last-saved-position when there’s none, my
	suggestion would be for it to be amended with an appropriate
	‘unless’ guard.

	Alternatively (or perhaps complementarily), a call to
	erc-log-save-all-buffers may be added to the
	erc-disconnected-hook’s default value.  (Please note that this
	alone, however, may be less reliable a measure.)

-- 
FSF associate member #7257