Fix #7400: Water class for tree tiles was not converted for old saves preventing industry creation.

As the information is always available from the tree ground type, unconditionally
update the map array for tree tiles.

src/tree_map.h

@@ -277,6 +277,7 @@ static inline void MakeTree(TileIndex t, TreeType type, uint count, uint growth,
 {
 	SetTileType(t, MP_TREES);
 	SetTileOwner(t, OWNER_NONE);
+	SetWaterClass(t, ground == TREE_GROUND_SHORE ? WATER_CLASS_SEA : WATER_CLASS_INVALID);
 	_m[t].m2 = ground << 6 | density << 4 | 0;
 	_m[t].m3 = type;
 	_m[t].m4 = 0 << 5 | 0 << 2;