Added test case to illustrate bogus conflicts detected if no files were merged, and untracked files exist in the workdir.
Only check for workdir conflicts if the index has merged files

Passing 0 as the length of the paths to check to git_diff_index_to_workdir
results in all files being treated as conflicting, that is, all untracked or
modified files in the worktree is reported as conflicting
Remove local unused index_repo variable