Fixed DatabaseCreation.get_test_db_clone_settings() for empty database name on SQLite.

Empty string should be considered an in-memory SQLite database.

django/db/backends/sqlite3/creation.py

@@ -53,7 +53,7 @@ class DatabaseCreation(BaseDatabaseCreation):
 
     def get_test_db_clone_settings(self, suffix):
         orig_settings_dict = self.connection.settings_dict
-        source_database_name = orig_settings_dict["NAME"]
+        source_database_name = orig_settings_dict["NAME"] or ":memory:"
 
         if not self.is_in_memory_db(source_database_name):
             root, ext = os.path.splitext(source_database_name)