Rearranging map groups copies maps incorrectly

[GriffinRichards]

Moving a map group up in the list copies the maps from the map group above its old position in the list. Moving map groups down in the list seems to work correctly. Only present on master.

[GriffinRichards]

Adding on to this, moving multiple groups at the same time doesn't work either (only the uppermost selected map group is moved, the rest are deleted).

[GriffinRichards]

And another, dropping a map group below the bottom of the list crashes Porymap