[pdf] Bounds check in skia_alloc_func

The allocator callback for zlib needs to check that items * size will
fit in size_t and return nullptr if not.

Conflicts:
- src/pdf/SkDeflate.cpp: just in header includes

Bug: 349678452
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/888996
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4ac6d5834d4d701232e98745a58815fb2ac9cd75)
Merged-In: Id1a30592d435bd0de4630e7047f26b0dc17654fc
Change-Id: Id1a30592d435bd0de4630e7047f26b0dc17654fc