Prevent fetching already fetch changesets from already initialized branches

by removing branches when the changeset of child branch
is alredy found in the repository
Fix crash when parent tfs is not found

because the branch is a pure git branch
Merge pull request #671 from pmiossec/fix_crash_list_empty

Fix crash when parent tfs is not found
Merge pull request #675 from pmiossec/improve_init_when_renames

Prevent fetching already fetch changesets from already initialized branches
Handle error case  where no merge info is returned by QueryMerges