Fix list variables returning null

[TPGamesNL]

Description

(the change is at L300)

With a list variable like: {_a::b::c} = 1, without a value at {_a::b}, the expression {_a::*} would return an array of size 1 instead of 0.

Test code:

command /test:
	trigger:
		set {_a::b::d} to 1
		set {_a::c::d} to 1
		message "size: %size of {_a::*}%"
		message "values: %{_a::*}%"

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Target Minecraft Versions: any
Requirements: none
Related Issues: #2600