Explicitly cast ints in SkSTArray.
Explicitly cast ints in SkSTArray.

The compiler can complain about these signed to unsigned conversions.
Explicitly cast them in initWithPreallocatedStorage to match the way
this is already done in init [0].

[0] 311b64801374c6eac36197a2e68834e00151f129 "pack SkTArray"

Change-Id: I0f723094fd356f9c5971b35998c4ecd59c09332f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/536099
Reviewed-by: Florin Malita <a8262bf13ea8c26821e91ea9bca6740a77c96dcd@google.com>
Commit-Queue: Ben Wagner <53965154ffeecc4a10886eab9259e95965f2979a@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia