Bluetooth: Mesh: Fix not sending all segments through the Friend Queue

The code was incorrectly bailing out with "return 0" rather than
continue. Also, it was incorrectly making a reference to
tx->seg[seg_o] since when a PDU goes through the friend queue we don't
use the usual retransmission mechanism.

Fixes: #17932

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>