[Interest] QTextLayout::isValidCursorPosition() gives different result in Qt 5.3.0 vs Qt 4.8.6?

[John Weeks]

I don't know very much about QTextLayout...

With this code copied from our very large application, when qtext contains "A":

 	QTextLayout qLayout(qtext, f);
	qLayout.beginLayout();
	QTextLine qLine= qLayout.createLine();	// If there is no text left to be inserted into the layout, the QTextLine returned will not be valid (isValid() will return false).
	haveLine= qLine.isValid();
	if( haveLine ) {
		qreal width= std::numeric_limits<double>::infinity();   //INFINITY;
		qLine.setLineWidth(width);	// everything on one line.
		qLine.setPosition(QPointF(xPos, yPos));	// top/left of first character
	}
	qLayout.endLayout();

	qDebug() << "qLayout.isValidCursorPosition(0) =" << qLayout.isValidCursorPosition(0);
	qDebug() << "qLayout.isValidCursorPosition(1) =" << qLayout.isValidCursorPosition(1);
	qDebug() << "qLayout.isValidCursorPosition(2) =" << qLayout.isValidCursorPosition(2);

When built with Qt 4.8.6, I get 
qLayout.isValidCursorPosition(0) = true 
qLayout.isValidCursorPosition(1) = false 
qLayout.isValidCursorPosition(2) = false 

whereas with Qt 5.3.0 I get
qLayout.isValidCursorPosition(0) = true
qLayout.isValidCursorPosition(1) = true
qLayout.isValidCursorPosition(2) = false

It seems like the Qt 5 output makes sense- the position after the last (only) character on the line should be a valid cursor position (that's where the next character typed will go, right?). But just in case this is a bug in Qt 5, I'd like to avoid changing the code to accommodate a bug...

-John Weeks