Fix (speculative) nullptr arithmetic #986

Job	Run time
Build and test cmake:gcc9	31s
Build and test cmake:clang15	32s
Build and test cmake:clang:asan	41s
Build and test cmake:clang:tsan	45s
Build and test cmake:clang:ubsan	52s
Build and test cmake:qemu-arm-neon-gcc	1m 9s
Build and test cmake-osx:clang	21s
Build and test cmake-osx:gcc	25s
Build and test cmake-win64:msvc-rel	1m 20s
Build and test cmake-win64:msvc-dbg	1m 26s
Build and test fuzz:clang	33s
Build and test python3.10:clang	1m 41s
Build and test python3.10-win	48s
Build and test maven	23s
Build and test bazel:root	40s
Build and test bazel:go	1m 0s
Build and test bazel:java	2m 3s
Build and test bazel:research	43s
Build and test bazel-osx:root	47s
Build and test bazel-osx:go	1m 10s
Build and test bazel-osx:java	2m 13s
Build and test bazel-osx:research	49s
Build and test bazel-win:root	2m 3s
Build and test bazel-win:java	2m 7s
Build and test bazel-win:research	1m 52s
	26m 54s

Provide feedback