♻️ Remove _misource access from AddLightningWall (#5098)

Source/missiles.cpp

@@ -1378,12 +1378,19 @@ void AddLightningWall(Missile &missile, const AddMissileParameter &parameter)
 	UpdateMissileVelocity(missile, parameter.dst, 16);
 	missile._miAnimFrame = GenerateRnd(8) + 1;
 	missile._mirange = 255 * (missile._mispllvl + 1);
-	if (missile._misource < 0) {
+	switch (missile.sourceType()) {
+	case MissileSource::Trap:
 		missile.var1 = missile.position.start.x;
 		missile.var2 = missile.position.start.y;
-	} else {
-		missile.var1 = Players[missile._misource].position.tile.x;
-		missile.var2 = Players[missile._misource].position.tile.y;
+		break;
+	case MissileSource::Player: {
+		Player &player = *missile.sourcePlayer();
+		missile.var1 = player.position.tile.x;
+		missile.var2 = player.position.tile.y;
+	} break;
+	case MissileSource::Monster:
+		assert(missile.sourceType() != MissileSource::Monster);
+		break;
 	}
 }