In TStreamerBase::InitStreaming don't search on checksum when we can't.
In TStreamerBase::InitStreaming don't search on checksum when we can't.

This is one of two fixes for ROOT-6765 (and possibly ROOT-6779)

Conflicts:
	core/meta/src/TStreamerElement.cxx

tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot,tc3t/qoot