Improvements to error handling:
- Stopped mixing DOS and Exec error codes!
- Avoid dereferencing null pointers in FAT entry functions if FAT
blocks can't be read.
- Return a success indication from FAT-entry-setting functions.
- Handle failure to allocate cache and FAT buffers.
- Flush buffers to disk immediately after formatting and check it succeeds.
- Show DOS device name in requesters if volume name is unknown.
git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@50974 fb15a70f-31f2-0310-bbcc-cdcc74a49acc