NamedWindows: when converting the text property, handle the empty list.
NamedWindows: when converting the text property, handle the empty list.

This fixes a "Prelude.head" exception observed with windows that have no title.
Reproduce by placing several windows in the tabbed layout, then starting
'xterm -name ""'.  Thanks to Andrea for pointing out the issue.

darcs-hash:20080502104249-a5988-c460b42456d65ad71016a7423e713b8250f1aa5c

yzhou61/xmonad-contrib,yzhou61/xmonad-contrib,yzhou61/xmonad-contrib