dont memmove a null pointer. caught by bounds checker.

main/streams.c

@@ -469,7 +469,7 @@ static void php_stream_fill_read_buffer(php_stream *stream, size_t size TSRMLS_D
 		/* no; so lets fetch more data */
 		
 		/* reduce buffer memory consumption if possible, to avoid a realloc */
-		if (stream->readbuflen - stream->writepos < stream->chunk_size) {
+		if (stream->readbuf && stream->readbuflen - stream->writepos < stream->chunk_size) {
 			memmove(stream->readbuf, stream->readbuf + stream->readpos, stream->readbuflen - stream->readpos);
 			stream->writepos -= stream->readpos;
 			stream->readpos = 0;