media: dw2102: Fix null-ptr-deref in dw2102_i2c_transfer()

In the Linux kernel, the following vulnerability has been resolved: media: dw2102: Fix null-ptr-deref in dw2102_i2c_transfer() In dw2102_i2c_transfer, msg is controlled by user. When msg[i].buf is null and msg[i].len is zero, former checks on msg[i].buf would be passed. Malicious data finally reach dw2102_i2c_transfer. If accessing msg[i].buf[0] without sanity check, null ptr deref would happen. We add check on msg[i].len to prevent crash. Similar commit: commit 950e252cb469 ("[media] dw2102: limit messages to buffer size")