[3.0] Let the Post event button reach the event form

[albertlast]

Description

The Post event button on a topic (?action=post;calendar;msg=N;topic=N.0, added by Display.php) has never reached the form. It fatals with "Invalid date.", every time, on every forum.

Post::initiateEvent() hands the request to Event::setRequestedStartAndDuration() before constructing the event. That helper is the one used when an event is saved, so it insists on being given a date and calls fatalLang('invalid_date') when it cannot find one. Nothing gives it one here: the button is a plain link, so there is no post data at all. (It only ever reads $_POST, so a date in the query string would not help either.)

Removing that uncovered a second fatal in the same few lines. The properties array named title and location unconditionally, passing null when the request had not supplied them:

'title' => isset($_REQUEST['evtitle']) ? Utils::htmlspecialchars(...) : null,

Event::$title and Event::$location are both public string with a '' default, so the constructor rejects the null with "Cannot assign null to property SMF\Calendar\Event::$title of type string". Absent means '' here, not null.

Calendar::post() draws the unlinked version of this same form and has neither problem, because it simply does new Event(-1) and lets the constructor fill in the defaults. This makes initiateEvent() behave the same way: name only the properties the request actually gave, and only ask for the requested start when the request carries one — which is exactly the case that matters, a failed post being redisplayed.

There is a third one behind these two, already fixed in #9405: with both of the above out of the way the form next dies on "Object of type SMF\TimeInterval ... has not been correctly initialized" from Event::__construct(). Both PRs are needed before the button works; they are independent and can land in either order.

How this was tested

On a local 3.0 install, with #9405 merged in for the third fatal:

• ?action=post;calendar;msg=1;topic=1.0 now draws the Post Event form, defaulting to now, with no console errors and nothing in smf_log_errors.
• Filling in a title and saving writes the row and links it to the topic (id_topic and id_board both set), then redirects to the post.
• The redisplay path is unchanged: POSTing the form with an invalid subject and start_date=2027-03-04, start_time=09:30 comes back with those values still in the fields, so the guard lets setRequestedStartAndDuration() run whenever the request actually has a date.
• Before this change, all three of those are the "Invalid date." error page.

Issues References (Fixes|Related|Closes)

Related: #9405