RTEMS | dosfs: A full 8.3 name overflows the short name buffer (#5723)

[Sebastian Huber (@sebhub)]

Issue created by Sebastian Huber: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5723



`msdos_short_entry_to_utf8_name()` gives the buffer of the formatted short name
`MSDOS_NAME_MAX_WITH_DOT` bytes. That is the length of a full 8.3 name and
leaves no room for the terminating null character which
`msdos_format_dirent_with_dot()` writes. A directory entry which uses all eight
base and all three extension characters writes one byte past the buffer.

The effect is visible where the compiler places a live variable in that byte.
On `microblaze` the byte holds the low byte of the destination size, which
becomes zero. The converter then produces nothing,
`msdos_find_file_in_directory()` skips the entry, and every lookup of that name
fails with `ENOENT`. `readdir()` still reports the entry, so such a file cannot
be opened, removed or renamed.

Found while running the full test suite on eleven simulators. This description
was created with Claude Code assistance.

-- 
View it on GitLab: https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5723
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