initialize pixel buffer inside of makeSurface for SDL_SWSURFACE

* initialize pixel buffer inside of `SDL.makeSurface` for SDL_SWSURFACE (added test for this)
* removed `flags |= 1; // SDL_HWSURFACE - this tells SDL_MUSTLOCK that this needs to be locked` from `SDL.makeSurface`. SDL_MUSTLOCK is #define'd to return 1 always
* removed some old comments describing offsets from before we had C_STRUCTS.*
* fixed potential issue in SDL_UnlockSurface where the lock count could get off if called multiple times once already unlocked

Ran browser tests.