Fix "smart" placement bug when there are shaded windows in other workspaces
Bug overview:
New windows are sometimes mis-placed when the "smart" algorithm is used.
How to reproduce it:
be sure (with WPrefs.app, for instance) to use the so-called "smart"
window placement algorithm. In an empty workspace, open a first window
(for instance, an xterm). The window should appear at the upper left corner.
Shade it (hide its contents below its title bar by double-clicking on it)
and select another empty workspace. Open another window. Instead of placing
it at the exact same place as the first window, wmaker places the new
window a little bit lower, or frankly to the right.
Explanation and correction:
when placing a new window, wmaker avoided all shaded windows, instead of
only avoiding the shaded windows on the active workspace.