[scudo] Use nullptr instead of integer-to-pointer cast am: d1f799403b am: 94150297cd am: 58033868c9

Original change: https://android-review.googlesource.com/c/platform/external/scudo/+/2045287

Change-Id: I6c3ac27a87e1a4c035d8d11b6fb8ce20c07d893d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>