avoid rlc am segfualt issue

openair2/LAYER2/RLC/AM_v9.3.0/rlc_am_rx_list.c

@@ -940,7 +940,7 @@ rlc_am_rx_check_all_byte_segments(
   rlc_am_pdu_info_t  *pdu_info_p        = &((rlc_am_rx_pdu_management_t*)(tb_pP->data))->pdu_info;
   mem_block_t        *cursor_p        = NULL;
   mem_block_t        *first_cursor_p  = NULL;
-  rlc_sn_t            sn              = pdu_info_p->sn;
+  rlc_usn_t            sn              = pdu_info_p->sn;
   sdu_size_t          next_waited_so;
   sdu_size_t          last_end_so;
 
@@ -971,6 +971,9 @@ rlc_am_rx_check_all_byte_segments(
   // the so field of the first PDU should be 0
   //cursor_p = list.head;
   //we start from the first stored PDU segment of this SN
+  if(cursor_p->data == NULL){
+    return;
+  }
   pdu_info_p = &((rlc_am_rx_pdu_management_t*)(cursor_p->data))->pdu_info;
 
   // if the first segment does not have SO = 0 then no need to continue
@@ -987,6 +990,9 @@ rlc_am_rx_check_all_byte_segments(
   while (cursor_p->next != NULL) {
     //msg("rlc_am_rx_check_all_byte_segments(%d) @4\n",sn);
     cursor_p = cursor_p->next;
+    if(cursor_p->data == NULL){
+      return;
+    }
     pdu_info_p = &((rlc_am_rx_pdu_management_t*)(cursor_p->data))->pdu_info;
 
     if (pdu_info_p->sn == sn) {