message: Use nextSiblingElement instead of nextSibling
  We are only interested in XmlElement objects, not the more generic
  XmlNode.
diff: @@ -493,7 +493,7 @@ void TileMap::deserialize(NAS2D::Xml::XmlElement* element)
  mapViewLocation({view_x, view_y});
  currentDepth(view_depth);
  - for (XmlNode* mine = element->firstChildElement("mines")->firstChildElement("mine"); mine; mine = mine->nextSibling())
  + for (XmlNode* mine = element->firstChildElement("mines")->firstChildElement("mine"); mine; mine = mine->nextSiblingElement())
  {
  int x = 0, y = 0;
  @@ -519,7 +519,7 @@ void TileMap::deserialize(NAS2D::Xml::XmlElement* element)
  }
  // TILES AT INDEX 0 WITH NO THINGS
  - for (XmlNode* tileNode = element->firstChildElement("tiles")->firstChildElement("tile"); tileNode; tileNode = tileNode->nextSibling())
  + for (XmlNode* tileNode = element->firstChildElement("tiles")->firstChildElement("tile"); tileNode; tileNode = tileNode->nextSiblingElement())
  {
  int x = 0, y = 0, depth = 0, index = 0;
  