djpeg: Fix PPM output regression w/ color quant. Regression caused by aa7459050d7a50e1d8a99488902d41fbc118a50f Fix based on: https://github.com/sinic/libjpeg-turbo/commit/03fbacb8ebf1fffc3f2d2db26ddf4db8b1f6aa7b Closes #310