Blender Git Loki

VSE: Fix disk cache potentially overwriting blend file

When disk cache path is same as blend file path, with Unix-like systems
blend file can be overwritten by disk cache directory.
This was caused by `BLI_delete(path, false, true)` when path points to
file. On Windows this would result in error message and file would not
be deleted. On Linux, file is deleted and then overwritten with cache
directory.

To further minimize chance of removing blend file, append disk cache
path with `_seq_cache` suffix.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D11217