For one pass CBR: only check for updating refresh_golden
if ext_refresh_frame_flags_pending is not set (i.e., == 0).
And move the resetting of ext_refresh_frame_flags_pending = 0
down to after the encode_loop (and account for dropped frames).

This is to prevent changing refresh_golden flga when the user
supplies the reference/update flags.

Change-Id: I4d87b3e705ba43f243667e367503b585c61e2a54