Fixed crashes on srteam write.
Fixed crashes on srteam write.

 * Added check if stream and stream->buffer are not NULLs in
   `axutil_stream_write_basic` function.

 Sometimes stream->buffer is NULL. This causes segfault in
 memcpy function.

Denisss025/wsfcpp,Denisss025/wsfcpp,Denisss025/wsfcpp,Denisss025/wsfcpp,Denisss025/wsfcpp,Denisss025/wsfcpp,Denisss025/wsfcpp