Fix bug FM-826. Here is a summary: when the data in a fragment is mangled, http streaming starts to encounter bad box type and bad box size, such as 30 billion bytes. For any "unfamiliar" box type, http streaming will skip the box based on the box size. However, there is a flaw in HTTPNetStream that cast the bytes needed to int type. This will generate a negative value for bytes needed, thereby breaking the logic. The fix is simple, change from int type to Number type. The if clause is just a safe guard.
