Fix (speculative) nullptr arithmetic #987

Job	Run time
Build and test cmake:gcc9	34s
Build and test cmake:clang15	37s
Build and test cmake:clang:asan	59s
Build and test cmake:clang:tsan	48s
Build and test cmake:clang:ubsan	46s
Build and test cmake:qemu-arm-neon-gcc	2m 10s
Build and test cmake-osx:clang	25s
Build and test cmake-osx:gcc	29s
Build and test cmake-win64:msvc-rel	1m 19s
Build and test cmake-win64:msvc-dbg	1m 23s
Build and test fuzz:clang	31s
Build and test python3.10:clang	1m 58s
Build and test python3.10-win	1m 0s
Build and test maven	30s
Build and test bazel:root	38s
Build and test bazel:go	1m 5s
Build and test bazel:java	2m 14s
Build and test bazel:research	39s
Build and test bazel-osx:root	54s
Build and test bazel-osx:go	1m 13s
Build and test bazel-osx:java	2m 24s
Build and test bazel-osx:research	1m 4s
Build and test bazel-win:root	1m 59s
Build and test bazel-win:java	1m 17s
Build and test bazel-win:research	1m 55s
	28m 51s

Provide feedback