Fix (speculative) nullptr arithmetic #982

Job	Run time
Build and test cmake:gcc9	31s
Build and test cmake:clang15	38s
Build and test cmake:clang:asan	41s
Build and test cmake:clang:tsan	47s
Build and test cmake:clang:ubsan	44s
Build and test cmake:qemu-arm-neon-gcc	1m 7s
Build and test cmake-osx:clang	24s
Build and test cmake-osx:gcc	24s
Build and test cmake-win64:msvc-rel	37s
Build and test cmake-win64:msvc-dbg	1m 24s
Build and test fuzz:clang	29s
Build and test python3.10:clang	1m 43s
Build and test python3.10-win	32s
Build and test maven	26s
Build and test bazel:root	34s
Build and test bazel:go	1m 5s
Build and test bazel:java	2m 1s
Build and test bazel:research	26s
Build and test bazel-osx:root	44s
Build and test bazel-osx:go	1m 2s
Build and test bazel-osx:java	2m 18s
Build and test bazel-osx:research	1m 7s
Build and test bazel-win:root	1m 57s
Build and test bazel-win:java	1m 29s
Build and test bazel-win:research	1m 48s
	24m 58s

Provide feedback