This commit also changes the way the master index format detection
works, as the previous scheme could not distinguish VERSIONED from
WHIRLPOOL.
Signed-off-by: Graham <gpe@openrs2.org>
Spotted by Desetude.
I think this was an accident, as the similar Js5Index.Entry class can't
be a data class (as it contains an array).
Signed-off-by: Graham <gpe@openrs2.org>