avformat: Print "Consider increasing the value for analzeduration and probesize" even more often

The sample from ticket #2691 currently does not trigger "Consider increasing
the value for analzeduration and probesize" because the audio streams are
only added after calling estimate_timings(). Attached patch moves the message
below this function call.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
av_find_stream_info: initialize ret

This should fix hypothetical corner cases where it might have never been initialized before use

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat_find_stream_info: try to preserve the error code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat_find_stream_info: Do not consider no streams an error in flush codecs

This should have no functional effect, but allows a cleaner diff when moving it
down

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat_find_stream_info: move ret init down from flush codecs.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>