Assertion occures when terminating lte-softmodem process

Assertion occures when terminating lte-softmodem process.

Assertion (itti_desc.threads[destination_thread_id].task_state == TASK_STATE_READY) failed!
In itti_send_msg_to_task() /home/ubuntu/smbshare/work_naoi/20180702/master/common/utils/itti/intertask_interface.c:356
Task TASK_PDCP_ENB Cannot send message GTPV1U_ENB_TUNNEL_DATA_REQ (138) to thread 8, it is not in ready state (0)!

Sometimes this problem occurs, sometimes it does not occur. The probability of occurrence is about 50%.

This issue occures with following revision. develop branch Revision: 204488f8 Date: 2018/07/04 17:00:10