For some RCT2 parks the scenario name in the sv6 file is wrong, so take the real filename.

* Change how current title sequence is handled. It can either be
previewing a title sequence, or playing the preset.
* LoadMM and LoadRCT1 now save when script is saved.
* No more infinite failing to load loops.
* No more crashing when attempting to display "no save selected" in
title editor.
* Title editor now gracefully fails to preview a title sequence and lets
the user know with a context error.
* When preset title sequence fails to load, the preset will forcibly be
changed to the first sequence to successfully load.

Added changelog entries for last two items.

Fixes #5657

[ci skip]

Previously, it explicitly compared to -1, while _strcmpi can return
all integers.

The field `mechanic_status` is verified to be RIDE_MECHANIC_STATUS_HEADING
when entering the function

The checks were done in https://github.com/OpenRCT2/OpenRCT2/pull/6576
but probably due to me later rearranging things, I got them wrong.