[DF] Call CleanUpTask even if event loop throws
[DF] Call CleanUpTask even if event loop throws

Even if something within the event loop throws, we still need to call
CleanUpTask to make sure SnapshotHelperMT::FinalizeTask gets called,
to avoid teardown issues due to input and output TTrees of a Snapshot
being deleted concurrently.

root-mirror/root,olifre/root,root-mirror/root,karies/root,olifre/root,karies/root,olifre/root,olifre/root,karies/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,karies/root,karies/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,root-mirror/root