When from_psgi_response, a bug when headers are already output and charset is set...

When from_psgi_response, a bug when headers are already output and charset is set has been fixed.

[error] Caught exception in MyApp::Controller::Docs->stream_and_charset "You may not change the encoding once the headers are finalized at /usr/home/bokutin/code/reading/catalyst-runtime/lib/Catalyst/Response.pm line 202."
[warn] Useless setting a header value after finalize_headers and the response callback has been called. Since we don't support tail headers this will not work as you might expect.