The pointer header is an alias to msg and msg is being null checked.
However, if msg is null then header is also null and this can lead to
a null pointer dereference on the assignment type = header->type. Fix
this just using header->type after the null check and removing the need
for type as it is only used once.

Addresses-Coverity: ("Dereference before null check")

Fixes: 3de16839 ("media: allegro: add explicit mail encoding and decoding")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>