iot/mqtt: Fix rlen_decode size check.

If receiving a malformed MQTT packet with less than 5 bytes it's
possible to get a read one byte behind buf.

Change-Id: I34425add57c937c8fd9df5bf7b72af092d6f5f32
Signed-off-by: Stig Bjørlykke <stig@bjorlykke.org>
1 file changed