If a file name is encoded in a different encoding than default input, current
implementation make image generation to be cancelled. As this can happen quite
frequent, due to files from discs or Windows partitions incorrectly mounted,
the best we can do is just ignore this, replacing the wrong character with a
'_'.
This has to ensure that file names are unique among all files in an iso
directory. Current implementation can be improved by using a hash table
to keep the names, instead of iterate over all children. An alternative
method, keeping children sorted all the time, thus allowing binary
search, has been considered but discarded.
Current implementation support up to 9,999,999 equal files per
directory.