Move the check for potentially infinite recursion to
xsltApplySequenceConstructor. In this function, both template and
func:function calls can be handled. This also checks for the following
case of infinite recursion in attribute sets found with afl-fuzz:

<x:attribute-set name="set">
    <x:attribute name="attr">
        <elem x:use-attribute-sets="set"/>
    </x:attribute>
</x:attribute-set>

Rename funcLevel to depth and check against maxTemplateDepth. I hope it
isn't a problem to rename an internal struct item.