A task can exist in the database but not have any log stored on disk yet.
This is now returned as `204 No Content` instead of an internal server
error.
The web interface is also adjusted to cope with this.
It returns 2048 bytes at most. It'll likely be less than that, as it will
ignore the first bytes until the very first newline (to avoid returning
cut-off lines). If the log file itself is 2048 bytes or smaller, return the
entire file.
The add-on code was copy-pasted from other addons and used the GPL v2
license, whereas by accident the LICENSE text file had the GNU "Affero" GPL
license v3 (instead of regular GPL v3).
This is now all streamlined, and all code is licensed as "GPL v3 or later".
Furthermore, the code comments just show a SPDX License Identifier
instead of an entire license block.
Instead of returning an error "error doing X", just return "doing X". The
fact that it's returned as an error object says enough about that it's
an error.
This also makes it easier to chain error messages, without seeing the
word "error" in every part of the chain.
