[fixed] v3.5.2: Magic factions' dragons can only upgrade while above land

[tomreyn]

This might be known, but it wasn't to me: Apparently dragons can only mutate to those dark dragons while they are above land, not water. This seems wrong to me - being always-in-the-air units there's no logical reason why they should not be able to upgrade in the air while they are above unwalkable water.

[tomreyn]

I just verified that this same issue is also present on r2525. When above water, it will always say 'Position invalid' when an upgrade is requested. It's not a matter of having enough resources.

[tomreyn]

This is fixed in r2526. Thanks titi!