Fixed toFront opertaion in LRU logic of base tile hashing. Tests now pass.

common/basetilehash.go

@@ -43,8 +43,11 @@ func (bth *BaseTileHash) toFront(entry *btHashEntry) {
 	}
 	entry.prev.next = entry.next
 	entry.next.prev = entry.prev
+
 	entry.next = bth.root.next
 	entry.prev = &bth.root
+
+	bth.root.next.prev = entry
 	bth.root.next = entry
 }