lib,rlc_am_nr: support also NACK ranges without SO_start/end. Fix for NACK ranges of sizee == 1

lib/src/rlc/rlc_am_nr.cc

@@ -833,6 +833,7 @@ void rlc_am_nr_tx::handle_control_pdu(uint8_t* payload, uint32_t nof_bytes)
            range_sn++) {
         rlc_status_nack_t nack = {};
         nack.nack_sn           = range_sn;
+        if (status.nacks[nack_idx].has_so) {
           if (range_sn == status.nacks[nack_idx].nack_sn) {
             // First SN
             nack.has_so   = true;
@@ -841,9 +842,10 @@ void rlc_am_nr_tx::handle_control_pdu(uint8_t* payload, uint32_t nof_bytes)
           } else if (range_sn == (status.nacks[nack_idx].nack_sn + status.nacks[nack_idx].nack_range - 1)) {
             // Last SN
             nack.has_so = true;
-          nack.so_start = 0;
+            // This might be first+last item at the same time, so don't change so_start here
             nack.so_end = status.nacks[nack_idx].so_end;
           }
+        }
         handle_nack(nack, retx_sn_set);
       }
     } else {