File loss due to program interruption before file closing

[HamzaHajeir]

Hi there

Thanks for the great library!

I've noticed a file loss if the program is interrupted at small time windows, where the file is opened, but not yet committed (via sync).

esp8266/Arduino#8155 is an example of file loss.

The fail comes due to erasing the file when opened in writing mode.

As mentioned in docs 'recover guarantee to the last well-known state of the file', I'm looking for solution for such loss, so:

1. Does it erases the file when opened with LFS_O_RDWR flag?
2. If it's erased in LFS_O_RDWR, Is there an available mechanism to do so?
3. If there's no available mechanism, could be there a new flag indicates to preserve the file content until the lfs_file_close call?

Potential similar issue:

#344

Thanks again.