Fix Unsigned-integer-overflow in MPEG4Extractor

Caused by the extractor reading unsigned-integer into a
signed-integer.
Also added check of Unsigned-integer-overflow.

Bug: 232242894
Test: Ran the fuzzer using the bug's testcase.
Change-Id: Ibb195ba86e7d68c3f2c43ed6a750b0569b7e7dbe
1 file changed