Merge branch 'ew/gc-auto-pack-limit-fix' into maint

"gc.autoPackLimit" when set to 1 should not trigger a repacking
when there is only one pack, but the code counted poorly and did
so.

* ew/gc-auto-pack-limit-fix:
gc: fix off-by-one error with gc.autoPackLimit

diff --cc builtin/gc.c
Simple merge