So, all frames and errors are correctly reported in order.
Also limit the numbers of error during draining to prevent infinite loop.

This fix fate failure with THREADS>=4:
  make fate-h264-attachment-631 THREADS=4
This also reverts a755b725.

Suggested-by: wm4, Ronald S. Bultje, Marton Balint
Reviewed-by: w4 <nfxjfg@googlemail.com>
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Muhammad Faiz <mfcc64@gmail.com>