core: clear image before rendering SVGs

In renderSVGIconWidth() the image was not cleared, leading
to garbage backgrounds. This should have affected the video
icons. Apparently, nobody is using them..?

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/qthelper.cpp

@@ -1739,6 +1739,7 @@ QImage renderSVGIconWidth(const char *id, int size)
 	QSvgRenderer svg{QString(id)};
 	QSize svgSize = svg.defaultSize();
 	QImage res(size, size * svgSize.height() / svgSize.width(), QImage::Format_ARGB32);
+	res.fill(Qt::transparent);
 	QPainter painter(&res);
 	svg.render(&painter);
 	return res;