datastream: fix readString
datastream: fix readString

Change-Id: If9e0131ae3c18bfa273ff6aca9dfb089e79f7209

vbarbaresi/libqi,aldebaran/libqi-java,aldebaran/libqi,aldebaran/libqi-java,bsautron/libqi,aldebaran/libqi,aldebaran/libqi-java,aldebaran/libqi