Fix "yadm clone" from within a subdir of $YADM_WORK

When running "yadm clone" from a subdirectory of $YADM_WORK, e.g. from
$HOME/Music, YADM failed to populate its working context: The list of
files returned by the subsequent "git ls-files --deleted" was empty then.

yadm

@@ -771,7 +771,7 @@ function clone() {
   configure_repo
 
   # then reset the index as the --no-checkout flag makes the index empty
-  "$GIT_PROGRAM" reset --quiet -- .
+  "$GIT_PROGRAM" reset --quiet -- "$YADM_WORK"
 
   if [ "$YADM_WORK" = "$HOME" ]; then
     debug "Determining if repo tracks private directories"