fix svg scaling

Due to the an image texture needing u, v (or x, y) having their types being int... but with an svg, its defined as floats. mWidth and mHeight are both integers. When they are divided, you'll get very small differences between the width and height ratio. It's possible for the width ratio to be just slightly smaller than the height ratio, but in order to prevent any chopping by a single line of pixel, the smaller of the two should always be selected.

See the same fix I pushed a while back ago to retropie https://github.com/RetroPie/EmulationStation/pull/749