CGE2: Make impossible to dereference nullptr in sndDigiStart().
CGE2: Eliminate inferred misuse of enums in Sprite::labVal().
CGE2: Fix comparing _spr->file against null in runCommand().
CGE2: Don't allow Sprite::step() to dereference nullptr-s.
CGE2: Fix possible string overflow in setEye().
CGE2: Fix possible string overflow in Bitmap's constructor.
CGE2: Fix possible string overflow in Hero::expand().
CGE2: Initialize every member in Talk's every constructor.
CGE2: Initialize _maxDist in Hero's constructor.
CGE2: Initialize _h and _w in every constuctor of Bitmap.
CGE2: Remove unused variable from System.
CGE2: Initialize _startGameSlot.
CGE2: Fix initVolumeSwitch().
CGE2: Rename _soundHandle to _sfxHandle.
CGE2: Rework sound system.
CGE2: Add checkMute().

This keeps the "Mute All" option of ScummVM and the music on/off and speech on/off buttons of Sfinx's toolbar in sync.
CGE2: Silence GCC warning.
Merge https://github.com/scummvm/scummvm