path.c: Don't discard the return value of vsnpath()

path.c: Don't discard the return value of vsnpath()

The git_snpath() and git_pathdup() functions both use the (static)
function vsnpath() in their implementation. Also, they both discard
the return value of vsnpath(), which has the effect of ignoring the
side effect of calling cleanup_path() in the non-error return path.

In order to ensure that the required cleanup happens, we use the
pointer returned by vsnpath(), rather than the buffer passed into
vsnpath(), to derive the return value from git_snpath() and
git_pathdup().

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>