fix OUString simplify

In my commit fb847101519ad74c02183672c04ebf1d700aae83
"simplify - use OUString::startsWith where possible"

I incorrectly converted
 if ( !aURL.isEmpty() && ( aURL[ 0 ] != '#' ) )
to
 if ( aURL.startsWith("#") )

Change-Id: I7fa3a814e13724dc65821e09c03db898b92626ec