#1007 Don't appear the gap of listheader whose label is empty

[Jumper Chen]

<window title="TEST" width="100%" id="test" height="220px">
<listbox id="listbox" width="500px" height="80px">
<listhead>
<listheader width="80px"></listheader>
<listheader width="60px"></listheader>
<listheader width="200px"></listheader>
<listheader align="right" width="50px"></listheader>
</listhead>
</listbox>
</window>

[Jumper Chen]

Logged In: YES
user_id=1684431
Originator: YES

Fixed since 5/23.