Issue description:

Unable to export as a image sequence on the latest commit android(self-build), it just only export as single image not sequence.

Steps to reproduce:

1. Create animation with at least 2 or more frames
2. Export as .png, select All Frames then click export
3. Choose a path in system file manager
4. Keep the name file blank, and click save
5. After that, a new single file named (invalid).png was created.