Remove potential panic in `split_init` #4353

Job	Run time
Check selected Tier 3 platforms (nightly)	4m 44s
Check (stable)	2m 36s
Check nightly-only targets (nightly)	25s
Check (nightly)	2m 37s
Check --no-default-features (nightly)	52s
Rustfmt	4s
Check (1.63)	2m 27s
Test rustix_use_experimental_asm (powerpc64le-linux)	1m 14s
Test rustix_use_experimental_asm (s390x-linux)	1m 14s
Test use-libc (ubuntu)	37s
Test use-libc (i686-linux)	58s
Test (ubuntu)	44s
Test use-libc (aarch64-linux)	56s
Test (ubuntu-20.04)	42s
Test use-libc (powerpc64le-linux)	1m 0s
Test (i686-linux)	1m 4s
Test use-libc (riscv64-linux)	57s
Test (aarch64-linux)	1m 6s
Test use-libc (s390x-linux)	52s
Test (powerpc64le-linux)	58s
Test use-libc (arm-linux)	52s
Test (riscv64-linux)	1m 4s
Test (s390x-linux)	1m 7s
Test (arm-linux)	1m 4s
Test (ubuntu-stable)	35s
Test (i686-linux-stable)	1m 14s
Test (aarch64-linux-stable)	56s
Test (riscv64-linux-stable)	56s
Test (s390x-linux-stable)	1m 7s
Test (powerpc64le-linux-stable)	57s
Test (arm-linux-stable)	1m 5s
Test (ubuntu-1.63)	1m 23s
Test (i686-linux-1.63)	1m 28s
Test (aarch64-linux-1.63)	1m 39s
Test (riscv64-linux-1.63)	1m 34s
Test (s390x-linux-1.63)	1m 30s
Test (powerpc64le-linux-1.63)	1m 39s
Test (arm-linux-1.63)	1m 39s
Test (macos-latest)	30s
Test (macos-12)	50s
Test (windows)	57s
Test (windows-2019)	58s
Test (musl)	36s
	51m 47s

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