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Spec isn't clear on this, but when we are doing short term ref pic sets
that are relative to existing ones, these can keep chaining and then
grow their size without bound. Seems reasonable to constrain this value
for the delta based ones just as for the fully declared ones.

Also fixes range validation for cpb_cnt.

Also fixes zero valued NumPicTotalCurr.

Also fixes overflow in SPS parsing.

BUG=b:153111783,chromium:1148504,chromium:1148698,chromium:1148863,
chromium:1148910
TEST=Fuzzer no longer crashes

Change-Id: I430f1fe2d4e4e5affe6caea80be6d01b84896b14
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2536851Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Jeffrey Kardatzke <jkardatzke@google.com>
Cr-Commit-Position: refs/heads/master@{#827449}