Fix use-after-free crash

[nyanpasu64]

Fixes #48. I've converted two NTFS drives and the program hasn't crashed.

Unfortunately, the resulting btrfs filesystem triggered a kernel warning and went into read-only mode after mere minutes of using digiKam's SQLite database on it.

[maharmstone]

Unfortunately, the resulting btrfs filesystem triggered a kernel warning and went into read-only mode after mere minutes of using digiKam's SQLite database on it.

Could you paste the output of btrfs check please? My guess is that this is something related to fsync...

[nyanpasu64]

Here are the kernel warnings and btrfs check --repair after the corruption (I do not have btrfs check --repair before the corruption): https://gist.github.com/nyanpasu64/830d9bd57bb3aa7999ebae105a0b2e96

I got an error and read-only disk, btrfs check found and repaired errors, but digiKam continued sending the disk into read-only mode even though btrfs check did not find errors.

I've restored a Clonezilla backup (didn't try ntfs2btrfs --rollback) and reverted my disk to NTFS for now. I could try reconverting and running btrfs check, but I'm not excited to risk data loss and gamble on Clonezilla working again (and Clonezilla will wear my SSD to an extent, ntfs2btrfs not so much).