Wayland: Fix decorations not always being created

If a window was initially fullscreen then it would not get an XDG
decoration object.  If the window was later switched to windowed mode it
would then get fallback decorations instead of XDG ones.

src/wl_window.c

@@ -633,6 +633,7 @@ static GLFWbool createShellObjects(_GLFWwindow* window)
             xdg_toplevel_set_maximized(window->wl.xdg.toplevel);
 
         setIdleInhibitor(window, GLFW_FALSE);
+    }
 
     if (_glfw.wl.decorationManager)
     {
@@ -654,10 +655,9 @@ static GLFWbool createShellObjects(_GLFWwindow* window)
     }
     else
     {
-            if (window->decorated)
+        if (window->decorated && !window->monitor)
             createFallbackDecorations(window);
     }
-    }
 
     if (window->minwidth != GLFW_DONT_CARE && window->minheight != GLFW_DONT_CARE)
     {