Assets with .PNG extension are not found by Studio

[AerunDev]

Description of the problem

If the user has .PNG files for a Pokémon sprite, the sprite won't be displayed and Studio will default to the "?".

What is the expected behaviour

If the user has .PNG files used for some Pokémon sprites, it should be displayed.

Steps to reproduce

• Go to Bulbasaur resources UI.
• Change the front default sprite by a .PNG sprite.
• See the "?" default asset.