MPEG4Extractor: Fix unsigned to signed overflow

Add a check to ensure that track's timescale(uint32_t) is within int32_t
bounds before creating MPEG4Source, which expects the timescale as an
int32_t.

Flag: EXEMPT bugfix

Bug: 401429404
Bug: 401422347

Test: ./mp4_extractor_fuzzer
Change-Id: Ia97ee13c7dab606b19dcbf99a9a633ec0ed36171