Fix tests if .bak file exists
Fix tests if .bak file exists

When a backup file exists FDO offers to restore the backed up
project. Previously we didn't implement the offer to restore which
resulted in failed tests when we ran the tests and a backup file
existed. This change replaces the NotImplementedException with a
(suitable) do-nothing implementation.

sillsdev/LfMerge,ermshiperete/LfMerge,ermshiperete/LfMerge,ermshiperete/LfMerge,sillsdev/LfMerge,sillsdev/LfMerge