ipv4: Check if dev_out is NULL in ip_route_output_slow()

Change-Id: If04a8e99942dbe7e099e736dc87c2a49e1e778f9
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>
ipv4: Skip calling fib_detect_death() if fib_dev is NULL

Change-Id: I1b8c6c7e79cb8a05b4b715ddb3299d74edef0e14
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>