Fix prefix/suffix of unaryExpression in AST xml

prefix and suffx of unaryExpressions seem to be always empty in AST xml.

For example, I got this for code `*i`:
```xml
<unaryExpression>
	<prefix></prefix> <!-- empty? -->
	<primaryExpression>
		<identifierOrTemplateInstance>
			<identifier>i</identifier>
		</identifierOrTemplateInstance>
	</primaryExpression>
	<unaryExpression>
		<primaryExpression>
			<identifierOrTemplateInstance>
				<identifier>i</identifier>
			</identifierOrTemplateInstance>
		</primaryExpression>
	</unaryExpression>
</unaryExpression>
```