avformat/options_table: Set the default maximum number of streams to 1000

Fixes CVE-2016-9561, Note the security relevance of this is disputed as
running out of memory can happen with valid files

Suggested-by: Andreas Cadhalpun <andreas.cadhalpun@googlemail.com>
Reviewed-by: Andreas Cadhalpun <andreas.cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
