store: fix ListMeta overflow check for negative Head

Author: bootjp

store/list_helpers.go

@@ -53,11 +53,10 @@ func marshalListMeta(meta ListMeta) ([]byte, error) {
 		return nil, errors.WithStack(errors.Newf("list meta contains negative len: %d", meta.Len))
 	}
 	// Recompute Tail from Head+Len to guarantee the invariant and detect overflow.
-	expectedTail := meta.Head + meta.Len
-	if meta.Len > 0 && ((meta.Head > 0 && expectedTail < meta.Head) || (meta.Head < 0 && meta.Len > math.MaxInt64+meta.Head)) {
+	if meta.Len > 0 && meta.Head > math.MaxInt64-meta.Len {
 		return nil, errors.WithStack(errors.Newf("list meta Head+Len overflows int64: head=%d len=%d", meta.Head, meta.Len))
 	}
-	meta.Tail = expectedTail
+	meta.Tail = meta.Head + meta.Len
 
 	buf := make([]byte, listMetaBinarySize)
 	binary.BigEndian.PutUint64(buf[0:8], uint64(meta.Head))  //nolint:gosec // Head can be negative after LPUSH; uint64 cast preserves bits