Fix sound regression
Meant to put bbuf[sample + start] += (byte) (samples[sample] >> 8);
-- instead I put bbuf[sample + start] = (byte) (samples[sample] >> 8);
and it broke certain sounds like 4214 (summoning obelisk?)
Also tried to compare 1:1 to the original code and see if anything else was removed. Restored one loop that didn't audibly make a difference in the few I compared, but I know it exists in 317 too so it's not an obfuscation thing. I brought it over just in case.