Files with more than one dir deep can't be edited on Windows #553

Inky versions affected: 0.15.2, 0.15.1

Steps to reproduce:

1. Create included file with more than one dir deep: First/Second/third.ink for example, and fill it with any ink content (knot, for example)
2. Restart Inky
3. Go to that file, add any text at the beginning
4. Save project
5. Restart Inky.
   Expected behaviour: content of the included file is same as when project closed.
   Actual behaviour: added text not saved, last bytes of an previous file content is duplicated instead.
   On linux this problem is not reprodusable.

ink_folders_bug_after_edit.zip

ink_folders_bug.zip

We found a walkaround: if file is edited as a single file, not a project part, all changes saves successfully. But this is very uncomfortable.
Update: bug can reproduce even with single directory deep files, but unstable in this case.