Improve data receiving in creaderasync example

Received data should be accumulated at each triggering of readyRead()
during wait timeout. Otherwise application may print out only last
portion of received data.

Change-Id: Ib4d72f70e333298bae31c0eb95d7639b5c4d177d
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>