net: 9p: avoid freeing uninit memory in p9pdu_vreadf

If some of p9pdu_readf() calls inside case 'T' in p9pdu_vreadf() fails,
the error path is not handled properly. *wnames or members of *wnames
array may be left uninitialized and invalidly freed.

Initialize *wnames to NULL in beginning of case 'T'. Initialize the first
*wnames array element to NULL and nullify the failing *wnames element so
that the error path freeing loop stops on the first NULL element and
doesn't proceed further.

Found by Linux Verification Center (linuxtesting.org).

Fixes: ace51c4d ("9p: add new protocol support code")
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Message-ID: <20231206200913.16135-1-pchelkin@ispras.ru>
Cc: stable@vger.kernel.org
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>