Fix index out of bound when height < 0 or > 255

Bug report by TNTUP, see #173

MinecraftClient/Mapping/ChunkColumn.cs

@@ -41,8 +41,15 @@ namespace MinecraftClient.Mapping
         /// <param name="location">Location, a modulo will be applied</param>
         /// <returns>The chunk, or null if not loaded</returns>
         public Chunk GetChunk(Location location)
+        {
+            try
             {
                 return this[location.ChunkY];
             }
+            catch (IndexOutOfRangeException)
+            {
+                return null;
+            }
+        }
     }
 }