Fix MSAN unitialized memory in vulkan memory allocator.
Fix MSAN unitialized memory in vulkan memory allocator.

Bug: skia:12821
Change-Id: Iaadc9c5d2723b0973e46e121f27d204c5cfaa657
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/494477
Auto-Submit: Greg Daniel <39df0a804564ccb6cf75f18db79653821f37c1c5@google.com>
Reviewed-by: Christopher Dalton <ef7fc3a08ada7d31f16e9a18b5f3c728256e041e@google.com>
Commit-Queue: Greg Daniel <39df0a804564ccb6cf75f18db79653821f37c1c5@google.com>

google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia