Key On bit of B0-B8 registers does not work

[smokku]

Seems like Key On bit of B0-B8 registers does not work.

I see in the opl3.c:1445 code that it is supposed to be handled by emulation,
but if I just write 0x0F to register B0 on a freshly reset opl3_chip, I get a sound out of emulator.