GHSA-8gj8-hv75-gp94: `SegQueue` creates zero value of any type

Affected versions of this crate called mem::zeroed() to create values of a user-supplied type T. This is unsound e.g. if T is a reference type (which must be non-null).

The flaw was corrected by avoiding the use of mem::zeroed(), using MaybeUninit instead.