split causes frame overlapping on all outputs beyond the first

[rawesomeawesome]

Describe the bug
When outputting with splitting to maintain filesize, all PPM files after the first don't have old frames cleared, resulting in visual garbage.

To Reproduce
Steps to reproduce the behavior:

1. enable splitting
2. render flipnote
3. view results 2+
4. See errors

Expected behavior
old frames should be cleared, resulting in clean flipnotes, as are produced when making singular outputs and the first flipnote of any batch.