potential crash on exit fix (can't tell if it actually fixes it or if…

… it is related)

src/simulation/Air.cpp

@@ -358,20 +358,25 @@ void Air::RecalculateBlockAirMaps()
 	for (int i = 0; i <= sim.parts_lastActiveIndex; i++)
 	{
 		int type = sim.parts[i].type;
+		if (!type)
+			continue;
 		// Real TTAN would only block if there was enough TTAN
 		// but it would be more expensive and complicated to actually check that
 		// so just block for a frame, if it wasn't supposed to block it will continue allowing air next frame
 		if (type == PT_TTAN)
 		{
 			int x = ((int)(sim.parts[i].x+0.5f))/CELL, y = ((int)(sim.parts[i].y+0.5f))/CELL;
-			bmap_blockair[y][x] = 1;
-			bmap_blockairh[y][x] = 0x8;
+			if (sim.InBounds(x, y))
+			{
+				bmap_blockair[y][x] = 1;
+				bmap_blockairh[y][x] = 0x8;
+			}
 		}
 		// mostly accurate insulator blocking, besides checking GEL
 		else if ((type == PT_HSWC && sim.parts[i].life != 10) || sim.elements[type].HeatConduct <= (rand()%250))
 		{
 			int x = ((int)(sim.parts[i].x+0.5f))/CELL, y = ((int)(sim.parts[i].y+0.5f))/CELL;
-			if (!(bmap_blockairh[y][x]&0x8))
+			if (sim.InBounds(x, y) && !(bmap_blockairh[y][x]&0x8))
 				bmap_blockairh[y][x]++;
 		}
 	}