[GAME] func_precipitation clamp flag does not work as expected for particle snow and ash

[JillCrungus]

Describe the bug

When using func_precipitation with the "Particle Ash" or "Particle Snow" precipitation types, the particles emitted will not adhere to the bounds of the brush as expected when the "Clamp precipitation to brush bounds" flag is active.

Steps to reproduce

Steps to reproduce the behavior:

1. Create a map with a func_precipitation shaped such that the effect is only expected to occur in a specific bounds
2. Set the precipitation type to Particle Snow or Particle Ash and ensure that "Clamp precipitation to brush bounds" is enabled.
3. Compile the map and observe that the particles fall outside of the bounds of the brush

Expected behavior

It is expected that all the particle precipitation types properly obey this flag and adhere to the bounds of the brush. The rain effects appear to correctly obey it.

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Additional context

Here is a simple map made to demonstrate an effect of precipitation falling through a hole in a roof:

When compiled with the rain effects, this appears more or less as expected.

But with the snow or ash effects, it does not work.

You get the same result even if you attempt to further reign in the brush:

Which again, works as expected for rainfall: