HPCC-11002 Fix Regression in 5.0 dataset with xpath('Name')

Fix that any xpath that resulted in a xml nesting tag with a blank name would
have created an unnamed tag of the form &lt;>&lt;/>.

Also fix recursive calls to outputBeginNested() were not passing along current value for doIndent.

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>