message: fix http_client_coro crash when upload file without post data.
diff: @@ -942,7 +942,7 @@ static int http_client_coro_send_http_request(zval *zobject TSRMLS_DC)
  int content_length = 0;
  //post data
  - if (Z_TYPE_P(post_data) == IS_ARRAY)
  + if (post_data && Z_TYPE_P(post_data) == IS_ARRAY)
  {
  SW_HASHTABLE_FOREACH_START2(Z_ARRVAL_P(post_data), key, keylen, keytype, value)
  if (HASH_KEY_IS_STRING != keytype)
  @@ -994,7 +994,7 @@ static int http_client_coro_send_http_request(zval *zobject TSRMLS_DC)
  http_client_append_content_length(http_client_buffer, content_length + sizeof(boundary_str) - 1 + 6);
  //post data
  - if (Z_TYPE_P(post_data) == IS_ARRAY)
  + if (post_data && Z_TYPE_P(post_data) == IS_ARRAY)
  {
  SW_HASHTABLE_FOREACH_START2(Z_ARRVAL_P(post_data), key, keylen, keytype, value)
  if (HASH_KEY_IS_STRING != keytype)
  