HLTResultMTMaker: Disable StreamTagMaker if not configured in python
The default value of the HLTResultMTMaker.StreamTagMaker property is empty and the result maker should work just fine (and do basically nothing) in this case. This was broken after !33290 (merged) and is fixed here. If the property is empty, the StreamTagMaker tool is initialised as disabled and an isEnabled()
check is added before it is used.
Fixes ATR-21556