Bug/sap xml parsing

The spot test data I was using just to validate parse_xml in isolation is below. However, do please validate that the module still functions as you'd expect. You should be able to just run it as-is.

(CC @nmonkee and @jvazquez-r7)


````xml
<items>
	<item>
		<NAME>name.txt</NAME>
		<SIZE>123</SIZE>
	</item>
	<item>
		<FOO>foobar</FOO>
		<SIZE>111</SIZE>
	</item>
	<item>
		<NAME>name2.txt</NAME>
		<SIZE>546</SIZE>
	</item>
	<item>
		<NAME></NAME>
		<SIZE>666</SIZE>
	</item>
	<item>
		<NAME>name3.txt</NAME>
		<SIZE></SIZE>
	</item>
	<item>
		<NAME></NAME>
		<SIZE></SIZE>
	</item>
</items>
````

Incidentally, here are the other modules that rely on Nokogiri:

````
$ grep -ril 'Nokogiri' modules/
modules/auxiliary/gather/apple_safari_webarchive_uxss.rb
modules/auxiliary/scanner/oracle/oracle_login.rb
````

Those should be fixed, too (but they're not using `Nokogiri::XML` which is at the root of the original problem implied in  26da7a6ee77490136e491dc8b6d3b99261ddc844 )