IndexOutOfRangeException thrown if Tileset is switched on painted Tilemap #763

Summary

An IndexOutOfRange exception is thrown if the selected Tilemap's Tileset is switched. This exception only occurs if the Tileset has been painted on with Tiles that have a higher index than the new Tileset's maximum index. I also noticed that sometimes the tile pallette is not updated with the new Tileset.

How to reproduce

• Create two Tilesets, one with more tiles than the other
• Create a Tilemap with the larger Tileset
• Paint on the Tilemap with the highest index Tile in the Tileset
• Set the Tilemap's Tileset to the smaller one by dragging it into the Tileset section of the Tilemap in the object inspector
• Try painting on the earlier painted tile

Workaround

• Don't switch the Tileset on a Tilemap that has already been painted on (this is probably a rare case anyway)
• If you want to switch the Tileset but don't care about the painted tiles, Set them all to the zero index tile (top left corner) before switching the Tileset

Analysis

• Exception is thrown at Tile.cs:291 when in the UpdateAutoTileCon method
• Problem seems to be that the Tilemap has tiles with invalid indexes on them
• Maybe there needs to be a check for these invalid tiles before executing any paint action on them to reset them to normal