Merge pull request #2103 from thomasonegd/master

fix socket nullptr bug

components/net/at/at_socket/at_socket.c

@@ -571,11 +571,17 @@ int at_connect(int socket, const struct sockaddr *name, socklen_t namelen)
 __exit:
 
     if (result < 0)
+    {
+        if (sock != RT_NULL)
         {
             at_do_event_changes(sock, AT_EVENT_ERROR, RT_TRUE);
         }
+    }
 
+    if (sock)
+    {
         at_do_event_changes(sock, AT_EVENT_SEND, RT_TRUE);
+    }
     
     return result;
 }
@@ -699,6 +705,8 @@ int at_recvfrom(int socket, void *mem, size_t len, int flags, struct sockaddr *f
 
 __exit:
 
+    if (sock != RT_NULL)
+    {
         if (recv_len > 0)
         {
             result = recv_len;
@@ -717,6 +725,7 @@ __exit:
         {
             at_do_event_changes(sock, AT_EVENT_ERROR, RT_TRUE);
         }
+    }
 
     return result;
 }
@@ -806,9 +815,12 @@ int at_sendto(int socket, const void *data, size_t size, int flags, const struct
 __exit:
 
     if (result < 0)
+    {
+        if (sock != RT_NULL)
         {
             at_do_event_changes(sock, AT_EVENT_ERROR, RT_TRUE);   
         }
+    }
     else
     {
         result = len;