[client] wayland: fix double xdg_toplevel role assignment in libdecor path

libdecor_decorate() already creates an xdg_surface and xdg_toplevel
internally for the frame. Calling xdg_surface_get_toplevel() again on
that same xdg_surface just to fetch the toplevel for icon handling
assigns the xdg_toplevel role to the underlying wl_surface a second
time, which is a protocol violation.

On GNOME Shell 50 (mutter) this is no longer tolerated: mutter
terminates the Wayland connection ("WL: error in client
communication"), and since libdecor_shellInit() waits for the initial
configure with a blocking, error-less libdecor_dispatch(-1) loop, the
client hangs forever with no window and no diagnostic output. This
made -DENABLE_LIBDECOR=ON (the default when libdecor-0 is present)
appear completely broken on current GNOME/Wayland.

Use libdecor_frame_get_xdg_toplevel() instead, which returns the
xdg_toplevel libdecor already owns, without requesting a second role
assignment.

Require libdecor-0 >= 0.1.1, which is available in Debian oldstable,
so the new accessor is guaranteed by the build dependency.

client/displayservers/Wayland/desktops/CMakeLists.txt

@@ -23,7 +23,7 @@ endfunction()
 # the first entry here is the default
 add_desktop(xdg)
 
-pkg_check_modules(LIBDECOR IMPORTED_TARGET libdecor-0)
+pkg_check_modules(LIBDECOR IMPORTED_TARGET libdecor-0>=0.1.1)
 if(LIBDECOR_FOUND)
   option(ENABLE_LIBDECOR "Build with libdecor support" ON)
 else()

client/displayservers/Wayland/desktops/libdecor/libdecor.c

@@ -145,9 +145,7 @@ static bool libdecor_shellInit(
   libdecor_frame_map(state.libdecorFrame);
 
   // Get the xdg_toplevel for icon setting
-  struct xdg_surface * xdgSurface = libdecor_frame_get_xdg_surface(state.libdecorFrame);
-  if (xdgSurface)
-    wlWm.xdgToplevel = xdg_surface_get_toplevel(xdgSurface);
+  wlWm.xdgToplevel = libdecor_frame_get_xdg_toplevel(state.libdecorFrame);
 
   if (fullscreen)
     libdecor_frame_set_fullscreen(state.libdecorFrame, NULL);