Strip .png from layer names in the Editor

[erikari]

If .png is included at the end of an attachment name, it will display correctly in the editor, but cause errors on export.
The editor could automatically strip it away. (or display an error, but it seems smoother to just fix it automatically)

Reference topic
Reference email: FMfcgzQfBsvQvtlcKbkGpMmLvQjszBCP

[NathanSweet]

4.3.56-beta