ivfenc: fix two-pass support of raw files

Commit 3245d46 "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

ivfenc.c

@@ -950,7 +950,7 @@ int main(int argc, const char **argv_)
             SHOW(kf_max_dist);
         }
 
-        if(pass == 0) {
+        if(pass == (one_pass_only ? one_pass_only - 1 : 0)) {
             if (file_type == FILE_TYPE_Y4M)
                 /*The Y4M reader does its own allocation.
                   Just initialize this here to avoid problems if we never read any