Clean up PNG and JPEG encoding properly #1355

Job	Run time
android	26m 30s
flash-samples	38s
docs	30s
air-samples (4.0.5)	3m 26s
html5-samples	1m 21s
air-samples (4.1.5)	3m 14s
ios	15m 15s
linux	16m 1s
air-samples (4.2.5)	3m 33s
macos	1h 11m 55s
air-samples (4.3.1)	3m 21s
windows	15m 7s
package-haxelib	2m 2s
hashlinkc-samples (windows-latest)	1m 55s
hashlink-samples (windows-latest)	39s
hashlinkc-samples (ubuntu-20.04)	1m 36s
neko-samples (3.4.7, windows-latest)	47s
hashlink-samples (ubuntu-20.04)	28s
hashlinkc-samples (macos-12)	1m 48s
neko-samples (3.4.7, ubuntu-20.04)	19s
hashlink-samples (macos-12)	41s
neko-samples (3.4.7, macos-12)	45s
neko-samples (4.2.5, windows-latest)	54s
neko-samples (4.2.5, ubuntu-20.04)	20s
neko-samples (4.2.5, macos-12)	43s
notify	0s
	2h 53m 48s

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