Fix Snabbdom assertions

[luwes]

2 assertions are failing for Snabbdom

[blankhart]

The issue is in the fast insertion path on this line, which assumes an append at afterNode. Instead, that block should append at a[start_i] || afterNode:

    if (start_i > end_i) { // old list exhausted; process new list additions
      for (; start_j <= end_j; start_b = b[++start_j]) {
        parent.insertBefore(start_b, a[start_i] || afterNode);  // not afterNode
      }
    }

[WebReflection]

@blankhart thanks!