Fix vehicle shadows remaining visible at zero alpha

[Dryxio]

Summary

Fix vehicle shadows remaining visible when the vehicle's alpha is 0.

Before/After

Motivation

An invisible vehicle could still be located by its shadow when using:
setElementAlpha(vehicle, 0)

The shadow should disappear together with the vehicle and return when its alpha is restored.
Follow-up to #5270.

Test plan

setElementAlpha(vehicle, 0) on a occupied/unoccupied vehicle.

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.

[FileEX]

Have you tested it after the latest commit?

[Dryxio]

Have you tested it after the latest commit?

Yes

Something I didn't notice though is in night time for example it seems that it draws shadow when you drive under lights sources (lamppost etc), my pr doesn't cover this yet. Will check now, it's likely CShadows::RenderExtraPlayerShadows

[Dryxio]

last commit fixes the extra shadows under light sources