fix to extract only the first frame (numbered 0)

Created originally on Bitbucket by daniel_fort (Daniel Fort)

Was already merged in Bitbucket before import, marked as merged by the import user

Source changeset not longer availableat the time of import. Commit listwill look empty

Resolves issue #2560 (closed)

Note that the issue wasn't really that mlv_dump -f... give one more frame than expected but that extracting only frame 0 wasn't possible.