zabbix_sender doesn't clean up its semaphores

Steps to reproduce:

Run zabbix_sender a few times in a row. Then look at the semaphores. Depending on the amount of semaphores the system has you will run out eventually.

Result:

Zabbix_sender will fail to send data to the Zabbix server. Stating that the system has run out of semaphores.

 Expected:
Normal zabbix_sender run.