chardev: Fix record/replay error path NULL deref in device creation

chardev: Fix record/replay error path NULL deref in device creation

qemu_chardev_set_replay() was being called in chardev creation to
set up replay parameters even if the chardev is NULL.

A segfault can be reproduced by specifying '-serial chardev:bad' with
an rr=record mode.

Fix this with a NULL pointer check.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Resolves: Coverity CID 1559470
Fixes: 4c193bb129dae ("chardev: set record/replay on the base device of a muxed device")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-ID: <20240828043337.14587-2-npiggin@gmail.com>