MPEG4Extractor.cpp: Add check for size == SIZE_MAX

If size == SIZE_MAX, the line:

  uint8_t *buffer = new (std::nothrow) uint8_t[size + 1];

ends up allocating zero bytes, which is obviously incorrect.

Change-Id: I7d44a66b67c590041572e25d1fbd1de94401a77f