`blocksort.rs`: fix a refactoring bug #153

Job	Run time
Clippy	11s
QEMU build & test (stable, ubuntu-latest, s390x-unknown-linux-gnu, s390x-linux-gnu-gcc, qemu-s390...	39s
Build and test (stable, ubuntu-latest, x86_64-unknown-linux-gnu)	32s
Clippy (--no-default-features --features="c-allocator")	11s
Miri	1m 10s
QEMU build & test (stable, ubuntu-latest, i686-unknown-linux-gnu, i686-linux-gnu-gcc)	28s
Build and test (msrv, ubuntu-latest, x86_64-unknown-linux-gnu)	37s
Clippy (--no-default-features --features="rust-allocator")	20s
Build and test (beta, ubuntu-latest, x86_64-unknown-linux-gnu)	39s
wasm32	20s
	5m 7s

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