For cached databases: clone the requested value to avoid problems.

src/cached.cr

@@ -45,7 +45,7 @@ class DODB::CachedDataBase(V) < DODB::Storage(V)
 		return nil
 	end
 	def [](key : Int32) : V
-		@data[key] rescue raise MissingEntry.new(key)
+		@data[key].clone rescue raise MissingEntry.new(key)
 	end
 
 	def []=(index : Int32, value : V)