only announce work area when it changes
only announce work area when it changes

Icewm was announcing _NET_WORKAREA and _WIN_WORKAREA every time
that the desktop changed.  This commit alters the behvaiour to
only announce the work area when it changes.

jinn-alt/icewm,dicej/icewm,bedna-KU/icewm,bedna-KU/icewm,dicej/icewm,jinn-alt/icewm,dicej/icewm,bedna-KU/icewm,jinn-alt/icewm,dicej/icewm