fix for crash with utf-8 encoded URLs from flashgot plugin

Crash info: ProgrammingError: You must not use 8-bit bytestrings unless you use a
text_factory that can interpret 8-bit bytestrings (like text_factory = str). It
is highly recommended that you instead just switch your application to Unicode strings.

Instead of swithcin the entire application to utf-8 only the input data encoding is set.