Commit 3245d463 "ivfenc: support reading/writing from a pipe" broke
support for two pass encodes of raw files when done in two
invocations of ivfenc. The raw image was only set up on pass 0,
which was never hit when running with --pass=2 --passes=2.

Change-Id: I6a9858be1a8998d5bd45331123b46b1baa05b379