SVG : refactor and simplify width/height+viewBox logic (https://www.w3.org/TR/SVG11/struct.html#SVGElement) + check `font_sizes_` size before accesing last element
SVG : refactor and simplify width/height+viewBox logic (https://www.w3.org/TR/SVG11/struct.html#SVGElement) + check `font_sizes_` size before accesing last element

tomhughes/mapnik,lightmare/mapnik,lightmare/mapnik,lightmare/mapnik,mapnik/mapnik,tomhughes/mapnik,tomhughes/mapnik,tomhughes/mapnik,lightmare/mapnik,mapnik/mapnik,mapnik/mapnik,mapnik/mapnik