fix at_client.c
fix at_client.c

hezlog/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread,nongxiaoming/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,hezlog/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,geniusgogo/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,nongxiaoming/rt-thread