Fix sound not disabled anywhere using ``sound'' option.

[imdjh]

When start without GB/GBC ROM provided in GBBOOTROM / GBCBOOTROM variable,
soundMasterEnabled variable is set by default.
A logic glitch would enable soundMasterEnabled variable anyway.

[imdjh]

With this patch, the actual memory taking & CPU ticking are saved.
I haven't taken a screenshot with my node-inspect testing, but I can tell it reduced (at least) 3MB in heap allocation.

Here's the node --prof with node-tick-processor output:

# Before patch with sound: false
 [JavaScript]:
   ticks  total  nonlib   name
   1891    3.0%   12.4%  LazyCompile: *min native math.js:152
   1744    2.7%   11.5%  LazyCompile: *GameBoyCore.executeIteration /home/djh/bum/letweplay-codes/weplay-emulator/node_modules/gameboy/index.js:5837
   1151    1.8%    7.6%  LazyCompile: *GameBoyCore.computeAudioChannels /home/djh/bum/letweplay-codes/weplay-emulator/node_modules/gameboy/index.js:5626
   1072    1.7%    7.0%  KeyedCallMegamorphic: args_count: 2

# After patch with sound: false
 [JavaScript]:
   ticks  total  nonlib   name
  12215    4.9%   22.2%  LazyCompile: *GameBoyCore.executeIteration /home/djh/bum/letweplay-codes/weplay-emulator/node_modules/gameboy/index.js:5837
   7313    2.9%   13.3%  KeyedCallMegamorphic: args_count: 2
   6657    2.7%   12.1%  KeyedCallMegamorphic: args_count: 1 {1}

[imdjh]

Hi, rauchg:

I found this PR would causing GB emulating freeze randomly. I have no idea why it happenes, but I think the results are the results that it reduced CPU tick in audio part of code.