This happens if someone manually downloads a regular datfile from
redump.org and puts it where Dolphin stores datfiles. Dolphin needs
"special" datfiles that contain fields for serials and versions.
Before this change, all discs (except Datel discs) would show up as
"Unknown disc" when using a regular datfile.
This was making it impossible to use the Redump.org integration
without first manually creating a Redump folder in the Cache folder.
https://bugs.dolphin-emu.org/issues/11885
The old implementation of this was not able to distinguish between
a title that had the common key index set to 1 because it actually
was Korean and a title that had the common key index set to 1 due to
fakesigning. This new implementation solves the problem by
decrypting a content with each possible common key and checking
which result matches the provided SHA-1 hash.
The problem that the old implementation causes has only been reported
to affect a certain pirated WAD of Chronos Twins DX (WC6EUP), but it's
possible that the problem would start affecting more WADs if we add
support for the vWii common key (which uses index 2). Adding support
for the vWii common key would also prevent us from using the simpler
solution of always forcing the index to 0 if the title is not Korean.
