Skip zero values in EditorPropertyFlags

[kleonc]

This PR makes the EditorPropertyFlags not create a checkbox for enum entries with zero value, like None = 0. Such created checkboxes were broken / not usable before anyway.

Resolves godotengine/godot-proposals#14023.

Note the above proposal is about C#, but the issue is not C# specific. In GDScript, @export_flags indeed prevents adding 0 value arguments:

but it could still be added manually e.g. using _validate_property:

@tool
extends Node

@export_flags("First:1", "Second:2", "Third:4") var flags: int = 0

func _validate_property(property: Dictionary) -> void:
	if property.name == "flags":
		property.hint_string += ",None:0"

Result for the script above:

Before v4.6.rc2.official [78c6632]	After this PR

[Repiteo]

Thanks!