WebAgg backend: Fix unbound variable error in get_diff_image#8656

Merged

QuLogic merged 2 commits intomatplotlib:masterfrom

cknd:feature_keep_buffer

May 23, 2017

Commits on May 23, 2017

keep the old buffer so we can return something when get_diff_image is called while self._png_is_old
cknd
committed
let get_diff_image return None and deal with it downstream
cknd
committed