Fix generation of BNode name for microdata when 'itemid' is given without a value.

Fix generation of BNode name for microdata when 'itemid' is given with an empty value.
This results in using the MD5 of "0" in the name of BNodes: 'nodecfcd208495d565ef66e7dff9f98764da'
An example of where this is a problem is https://www.youtube.com/channel/UCQNIKO3SwRcYnoiuSqKYbOA
'<div id="watch-container" itemid="" itemscope itemtype="http://schema.org/YoutubeChannelV2">'

Also added a check to ToolRunnerTest for no tools.