From 0732da59b75b45ba04b74735b7592dba5e45a86a Mon Sep 17 00:00:00 2001
From: Chris Lilley fcTL Frame Control Chunk
step as long as the result is guaranteed to be identical. For example, if the default image is included in the animation,
and uses a `blend_op` of `APNG_BLEND_OP_SOURCE`, clearing is not necessary because the entire output buffer will be
overwritten.
Note, at the end of the fcTL chunk is a 32-bit CRC checksum. The checksum is - calculated using the fcTL chunk and includes the 'fcTL' chunk type field.