Don't assume picture dimensions prior to conversion

This section of the ImagingComponent class calculates height and width based on the maxSize parameter prior to conversion

        if (pictureConversion.getMaxSize() != null) {
            size = ImageResizer.scaleToMax(size.x, size.y, pictureConversion.getMaxSize());
        }        pictureViewMap.put(PictureView.FIELD_WIDTH, size.x);
        pictureViewMap.put(PictureView.FIELD_HEIGHT, size.y); 

while the section after the conversion (callPictureConversionChain) determines the real height and width from the ImageInfo of the result image

        pictureViewMap.put(PictureView.FIELD_INFO, getImageInfo(viewBlob));

If the picture conversion returns something not matching the expected maxSize it leads to the picture height and width conflicting with the image info height and width. As it becomes common to contribute custom picture conversions (https://doc.nuxeo.com/nxdoc/how-to-contribute-a-command-line-converter/, https://doc.nuxeo.com/nxdoc/how-to-contribute-picture-conversions/) this code should avoid recording conflicting image metadata.