Add a test for all uninitialised data handles
Discussed in https://its.cern.ch/jira/browse/ATR-21690
A DataHandle cannot be contructed from an un-initialised key. However, this might not be discovered until late in an HLT job since the CF tree is not fully explored in most events.
Added a test to the AthAlgStartVisitor to ensure that all handles have been initialised, before the event loop begins.