Fixes: runtime warnings when trying to render 0-size icon

Task-number: QTBUG-37035
Change-Id: I014988cdb57a2001685a8d50d79ee103322ed021
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

src/plugins/iconengines/svgiconengine/qsvgiconengine.cpp

@@ -169,6 +169,9 @@ QPixmap QSvgIconEngine::pixmap(const QSize &size, QIcon::Mode mode,
     if (!actualSize.isNull())
         actualSize.scale(size, Qt::KeepAspectRatio);
 
+    if (actualSize.isEmpty())
+        return QPixmap();
+
     QImage img(actualSize, QImage::Format_ARGB32_Premultiplied);
     img.fill(0x00000000);
     QPainter p(&img);