MINOR: ssl: Release ssl_ocsp_task_ctx.cur_ocsp when destroying task

In the unlikely event that the OCSP udpate task is killed in the middle
of an update process (request sent but no response received yet) the
cur_ocsp member of the update context would keep an unneeded reference
to a certificate_ocsp object. It must then be freed during the task's
cleanup.

src/ssl_ocsp.c

@@ -840,6 +840,9 @@ void ssl_destroy_ocsp_update_task(void)
 
 	task_destroy(ocsp_update_task);
 	ocsp_update_task = NULL;
+
+	ssl_sock_free_ocsp(ssl_ocsp_task_ctx.cur_ocsp);
+	ssl_ocsp_task_ctx.cur_ocsp = NULL;
 }
 
 /*