Cookoff - Improve destroying vehicle post cookoff

[Cyruz143]

When merged this pull request will:

• When cookoff completes vehicles explode (depending on settings)

In it's currently implementation, when cookoff completes and you have destroyVehicleAfterCookoff enabled, there is a chance (based around _detonateAfterCookoff) that the vehicle will just change to the wreck model without an explosion. This looks a bit weird to be honest, the explosion hides the model change fairly well and looks a bit more natural.

If you have destroyVehicleAfterCookoff disabled and _detonateAfterCookoff is also false, this statement never runs so it shouldn't have any unwanted impact.

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