QTextDocument: HTML image width tag is not handled correctly when the width is supplied as a percentage

If HTML is set on a QTextDocument such as this: <img src="./test.png" width="50%" />

the image disappears. This can be worked around by supplying a pixel width - e.g. <img src="./test.png" width="50" />

or by specifying a pixel height and percentage width for scaling.

The image should be scaled horizontally even in no height is supplied.