PHP unit fixes

[Fredthelead]

• Added a try-catch clause in Utils.php and return false if feeded with bad XML - as dictated in the phpunit test.
• Fixed some typos where the scalar value false was misspelled.
• Replaced assertNotContains with assertStringNotContainsString when asserting strings.

[pitbulk]

Hi, @Fredrik82

I think the loadXML method should raise an exception if not able to load the XML.

[Fredthelead]

Hi, @Fredrik82

I think the loadXML method should raise an exception if not able to load the XML.

I agree. I was unsure if the unit-test was supposed to be considered as source of truth or not. I reverted that commit and added a try-catch in the unit test instead.