Error when parsing property assignment `scope.property = value`

[nndda]

Add error handling where regex_vars_match.names might not have [__OP], and default operator to empty string explicitly.

Theatre/addons/Theatre/classes/DialogueParser.gd

Lines 464 to 470 in 5bdfd04

	# Operator assignment type if used
	# += -= *= /=
	# + - * /
	var operator := regex_vars_match.get_string(
	regex_vars_match.names[__OP]
	)
	var operator_used := not operator.is_empty()