Add more extensions to the dummy texture loader
Add more extensions to the dummy texture loader

This should make headless exporting work in projects using textures
in any format.

Error messages should no longer appear when running a project
that used image formats that were previously not present in the list.

(cherry picked from commit 3007c7e2a3bd2f693e2e5d3a9cee8b8cbd320580)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot