webm_file,CheckCuesAlignmentList: reduce stack size

fixes:
shared/webm_file.cc:693:1: error: the frame size of 16752 bytes is
larger than 16384 bytes

Bug: b/150135466
Change-Id: Id9b6a52fb33108b3b310dd92ea56e77152545a0b
PiperOrigin-RevId: 157805347
1 file changed