Fixed disappearing of tile type on export/import

When exporting or importing a tileset, or when enabling any export
options that affect the tileset, the tileset is cloned. In the process
of cloning however, the tile types were not getting copied over.

See also change 8494cd6. Maybe there is
a way to avoid making such errors so easily?

Closes #2023

src/libtiled/tile.cpp

@@ -205,6 +205,8 @@ Tile *Tile::clone(Tileset *tileset) const
     c->setProperties(properties());
 
     c->mImageSource = mImageSource;
+    c->mImageStatus = mImageStatus;
+    c->mType = mType;
     c->mTerrain = mTerrain;
     c->mProbability = mProbability;