OleFileIO.open: must set ministream before loaddirectory

[decalage2]

See bug reported here: https://blog.didierstevens.com/programs/oledump-py/#comment-354333

Two issues:

1. OleFileIO.ministream is not set by init, but by open after calling loadfat and loaddirectory. init should set all the attributes.
2. loadfat and loaddirectory should use the option force_FAT when calling _open to avoid using the MiniFAT.

[decalage2]

Fixed in commits 04c20f8 and f71a4ad