pngquant: Skip if Larger

We shouldn't be making any files larger.  This is a check against that!

Note: This requires pngquant version 2.1.0 or newer.  I recommend installing the upstream version from here: https://github.com/pornel/pngquant/commits/master  simply clone ./configure and make.

Signed-off-by: Chet Kener <Cl3Kener@gmail.com>
Change-Id: I313efb3ccd52e26c3e7e0951579e23228363417d