If there are 3 or more known atoms in a row, it's likely that this is
actually MOV/MP4 even if we don't find any other known atoms. If 5 or
more are found then this is most certainly MOV/MP4 and we can return.
Also if a moov and mdat atom is found, this is definitely a MOV/MP4 file
and can be used as such, independent of anything else following the
mdat.
Fixes typefinding of various MOV files that have no `ftyp` atom but
otherwise a valid file structure followed by some garbage.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/1013>
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