aria-valuenow set incorrectly when only the second pane is sized #362

When size is set for the second of two panes only the gutter element has set aria-valuenow to *, which is not a valid value for this attribute and results in accessibility issues.

To reproduce, create this minimal boilerplate:

<as-split>
  <as-split-area></as-split-area>
  <as-split-area size="30"></as-split-area>
</as-split>

and check the .as-split-gutter element, now with aria-valuenow incorrectly set to *