Making MidiMessageSequence parameter const

I’m not sure if I can post stuff like this on forum, but could git repo host switch int MidiMessageSequence::getIndexOf (MidiEventHolder* const event) to int MidiMessageSequence::getIndexOf (const MidiEventHolder* const event)?

Looks like OwnedArray::indexOf() accept const parameter as well, so that should not be a problem.
I don’t feel experienced enough to make pull request, since I’m not sure it won’t drag anything behind it.

Thanks. I’ve fixed this on the develop branch.