commit-reach: terminate merge-base walk when one side is exhausted #28503

Job	Run time
config	7s
fuzz smoke test	1m 28s
win+Meson build	1m 16s
win build	5m 28s
rust-analysis	1m 33s
static-analysis	4m 53s
osx-meson (macos-14)	1h 18m 48s
osx-clang (macos-14)	1h 18m 48s
sparse	3m 35s
osx-gcc (macos-14)	1h 18m 48s
osx-reftable (macos-14)	1h 18m 48s
documentation	5m 20s
linux-sha256 (ubuntu:rolling)	23m 6s
linux-breaking-changes (ubuntu:rolling)	22m 22s
linux-leaks (ubuntu:rolling)	50m 9s
win+VS build	-1s
linux-reftable (ubuntu:rolling)	22m 16s
linux-reftable-leaks (ubuntu:rolling)	44m 9s
linux-TEST-vars (ubuntu:20.04)	27m 31s
debian-11 (debian:11)	15m 37s
linux-asan-ubsan (ubuntu:rolling)	42m 39s
fedora-breaking-changes-meson (fedora:latest)	55s
linux-meson (ubuntu:rolling)	2m 7s
almalinux-8 (almalinux:8)	18m 55s
linux-musl-meson (alpine:latest)	22s
linux32 (i386/ubuntu:focal)	32m 51s
win+VS test	-1s
win test (2)	8m 6s
win test (0)	11m 58s
win test (6)	10m 40s
win test (4)	9m 34s
win test (9)	7m 18s
win test (1)	5m 53s
win test (5)	32m 58s
win test (3)	10m 46s
win test (7)	6m 7s
win test (8)	7m 14s
win+Meson test	-1s
	12h 32m 22s

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