Handle app data consistently.
Handle app data consistently.

We used to drop app data iff the output was YUV420 or strip_metadata was
enabled. This fixes #100.

google/guetzli,google/guetzli,ianhuang-777/guetzli,ianhuang-777/guetzli,google/guetzli,guanzidashu/guetzli_ios_metal,dloeng/guetzli,szabadka/guetzli,dloeng/guetzli,ianhuang-777/guetzli,guanzidashu/guetzli_ios_metal,szabadka/guetzli,google/guetzli,dloeng/guetzli,guanzidashu/guetzli_ios_metal,ianhuang-777/guetzli,szabadka/guetzli,guanzidashu/guetzli_ios_metal