media: dvb-frontends: dib7090p: fix null-ptr-deref in dib7090p_rw_on_apb()

media: dvb-frontends: dib7090p: fix null-ptr-deref in dib7090p_rw_on_apb()

In dib7090p_rw_on_apb, msg is controlled by user. When msg[0].buf is null and
msg[0].len is zero, former checks on msg[0].buf would be passed. If accessing
msg[0].buf[2] without sanity check, null pointer deref would happen. We add
check on msg[0].len to prevent crash. Similar issue occurs when access
msg[1].buf[0] and msg[1].buf[1].

Similar commit: commit 0ed554fd769a ("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Signed-off-by: Alex Guo <alexguo1023@gmail.com>
Link: https://lore.kernel.org/r/20250616013231.730221-1-alexguo1023@gmail.com
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>