Prevent overflow when growing an SkRegion's RunArray

Bug: 350118416
Test: N/A -- speculative issue without repro case
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/894836
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:85802e6d648a7831a26cc856fa5e33da94ed23f0)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:521332e28acde551bb63dbd6829e7089d73533d8)
Merged-In: Iea27fe62ef97deb8a75e8dae276657d809223b57
Change-Id: Iea27fe62ef97deb8a75e8dae276657d809223b57