Export Sprite Sheet has invalid JSON Data path on subsequent exports

Describe the bug After exporting a sprite sheet and switching to another aseprite project: trying to export that one does not populate the JSON Data field with a usable default value.

To Reproduce Steps to reproduce the behavior:

1. Open two distinct Aseprite projects
2. Click on File -> Export Sprite Sheet on project A and export (see: first screenshot attached)
3. Switch to project B and open the File -> Export Sprite Sheet window again
4. The error occurs with the value of JSON Data being **filename** (see: second screenshot attached)
5. If you were to run the second export the output .png file will be exported successfully but the JSON file will be absent

Expected behavior The JSON Data field should default to a path name relative to the project name in the same manner as it does for the first export.

Screenshots

Project A Export:

Project B Export:

Aseprite & System (please complete the following information):

• Aseprite: v1.3.18.5-x64 (Steam)
• System: Windows 11 Pro 25H2
• Extensions: None except for a third-party dark theme