[next] Flat textures in PNG format don't display properly

2.2.13:

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This bug happens in both renderers.

Example WAD: PNGFlatBug.wad

!2104 (merged) seems to have introduced this issue.

changed milestone to %2.2.14

added Bug Regression Rendering labels

mentioned in commit d90c2ac4

mentioned in merge request !2448 (merged)

assigned to @Lactozilla

closed with merge request !2448 (merged)

mentioned in commit d6df0694

unassigned @Lactozilla