fixed #1020399 aka broken ShowDesktop, its an error to travers the

workspace-windowlist and deiconify each window coz that list is
modified each time a window is iconified. a copy of that list solves
the problem.

ChangeLog

@@ -1,7 +1,10 @@
 (Format: Year/Month/Day)
 Changes for 0.9.13
+*05/04/23:
+  * Fixed #1020399 aka broken ShowDesktop - command (mathias)
+    WorkspaceCmd.cc
 *05/04/22:
-  * clear maximized-Flags of a resized/moved Window (Mathias=
+  * clear maximized-Flags of a resized/moved Window (Mathias)
     Window.cc
   * fixed Iconified+Sticky Windows not shown in Iconbar (Mathias)
     (when in WorkspaceIcons-Mode

src/WorkspaceCmd.cc

@@ -185,8 +185,8 @@ void ShowDesktopCmd::execute() {
     if (screen == 0)
         return;
 
-    Workspace *space = screen->currentWorkspace();
-    std::for_each(space->windowList().begin(),
-                  space->windowList().end(),
+    Workspace::Windows windows(screen->currentWorkspace()->windowList());
+    std::for_each(windows.begin(),
+                  windows.end(),
                   std::mem_fun(&FluxboxWindow::iconify));
 }