DNN-5201 When reading XML with XmlReader, skip unknown elements safely

When using an XmlReader, trying to read content from a comment (such as
DesktopModuleInfo could do) will cause an exception.  On the other hand, if
there is an unexpected element, it needs to be read in order for the reader to
move to the next element.
Merge pull request #98 from bdukes/patch-4

DNN-5201 When reading XML with XmlReader, skip unknown elements safely