Problems with ambient_generic event `OnSoundFinished` (from mapbase)

[jason-e]

• An ambient_generic which is set to start playing on map load sets the timer for firing OnSoundFinished before the duration of the sound file is known (as if the file has not been fully precached or something), causing the event to fire instantly. Reloading the map or even loading a different map and then the original will cause the expected behavior to occur, which suggests the sound file/duration is still cached somewhere.

Less critically:

• The event is fired even for looping sounds, at the end of the first playthrough of the sound. It would probably be better if it only fired for one-shot sounds. Otherwise, it would be worth making sure the duration reported by the engine (used for the event timer) is based on the loop end cue point rather than the full file duration.
• The event timer is always (re)started when the entity is loaded from a save file (or upcoming savestates), even though the event timer is saved and restored by the save file. Even if this is skipped for save file loads, the event will probably not actually line up with the sound ending because the sound has to be replayed from the beginning on load -- we could use a way to play sound files starting from an arbitrary time, unless that's already a thing.

The OnSoundFinished event came from mapbase so we could just get rid of it entirely.

[braem]

Fixed the bug of OnSoundFinished firing at incorrect times, and disabled it for looping sounds.

@jason-e The only thing now is getting it working with save/load/savestates. I assume there needs to be some other work to look at this first, but we should be able to play sounds at arbitrary times yup!

[Gocnak]

@braem @jason-e we should probably split out the remaining things into a new issue here, as 0.9.7 tackles the first bullet point