builtin-add: fix unmatched pathspec warnings.
builtin-add: fix unmatched pathspec warnings.

"git add Documentation/" when Documentation directory exists
does not barf (as it should not), but "git add ." barfed when it
did not add anything.  This was because we checked for the path
prefix ("Documentation/" in the former case, and an empty string
in the latter case) for existence, and lstat("", &st) would say
"Huh?".

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git