When the layer type is missing, fType == -1 and we rely on unsigned
(size_t) underflow + check against the known types array size to catch
the condition.
The problem is SkToSizeT() itself asserts the input is a valid size_t,
and even if it didn't clusterfuzz would likely complain about
underflowing.
Refactor to check for negative values explicitly.
Bug: b/200660146
Change-Id: Iae74dca14ac0202ffcdd4449f0d470063916eff5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/493116
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
3e1354a592