Rollup merge of #95699 - SparkyPotato:master, r=dtolnay

fix: Vec leak when capacity is 0

When `RawVec::with_capacity_in` is called with capacity 0, an allocation of size 0 is allocated.
However, `<RawVec as Drop>::drop` doesn't deallocate, since it only checks if capacity was 0. Fixed by not allocating when capacity is 0.