Xml Empty Data Exception

Empty data generate an error because  on line:

https://github.com/skler/serializer/blob/d177ebdd35e7a1c6e525506d3e8926632f353a36/src/JMS/Serializer/XmlDeserializationVisitor.php#L86

libxml_get_last_error() returns false 
this should be done before changing the libxml state (or you need to reset it before throwing, which would mean doing useless stuff).