Fix and improve world ping bugs

[SokyranTheDragon]

• Prevent pinging invalid locations
  • This includes trying to ping space or planet locations that aren't part of playable world
• When finding a tile under a mouse failed, attempt again but snap to expandable world objects
  • This will properly handle finding world objects in space
  • This doesn't allow pinging empty locations in space, as GenWorld.MouseTile cannot select those
• Prevent drawing pings from planet layers that aren't currently active
• When sending map location, use PlanetTile.Invalid rather than a surface tile with ID of 0.
• When receiving pings, make sure that we received a valid ping location before accepting it