Improve the fixing of un-optimized M4A

[skyline75489]

For some songs, the current implementation does not fetch enough data for mdat to show up. This is one of the problematic songs:

Atom ftyp @ 0 of size: 32, ends @ 32
Atom free @ 32 of size: 112547, ends @ 112579
Atom free @ 112579 of size: 483674, ends @ 596253
Atom mdat @ 596253 of size: 6359629, ends @ 6955882
Atom moov @ 6955882 of size: 113172, ends @ 7069054
     Atom mvhd @ 6955890 of size: 108, ends @ 6955998
     Atom trak @ 6955998 of size: 69281, ends @ 7025279

The mdat was at 596253. However the first packet received is only 13667 bytes long. The current logic does not takes this scenario into consideration.