Don't access sgSFX if sound is not initialized

Source/effects.cpp

@@ -182,6 +182,8 @@ void PrivSoundInit(uint8_t bLoadMask)
 
 bool effect_is_playing(SfxID nSFX)
 {
+	if (!gbSndInited) return false;
+
 	TSFX *sfx = &sgSFX[static_cast<int16_t>(nSFX)];
 	if (sfx->pSnd != nullptr)
 		return sfx->pSnd->isPlaying();
@@ -204,6 +206,8 @@ void PlaySFX(SfxID psfx)
 {
 	psfx = RndSFX(psfx);
 
+	if (!gbSndInited) return;
+
 	PlaySfxPriv(&sgSFX[static_cast<int16_t>(psfx)], false, { 0, 0 });
 }