When a request max file size is relatively small, don't store moov header at the

beginning of a recorded mp4 file.

Trying to put the 'moov' box at the beginning of an mp4 file requires to reserve
some estimated space for 'moov'. The estimate can be larger or smaller than the
actual 'moov' size. When the estimate is larger, we could meet the file
size limit, although some space is wasted; but when the estimate is smaller than
the actual 'moov' size, we not only waste the reserved space but also have to
use extra space to write 'moov' space at the end of the file. In this case, often
the requested file size limit could be exceeded by a large margin.

This patch avoids putting the 'moov' box at the beginning when a file size limit
is explicitly requested.

Change-Id: I838443d08b5589f33f3c486c662195600e3edb9b
related-to-bug: 6697505