Set layer-shell size to 1,1 on first commit

The commit with no set_size was interpreted as having set_size of 0,0,
which is no longer valid if anchors are not set.

However, are just configuring our surface, not yet committing content.
As workaround, specify a bogus 1,1 size to begin with.

Closes: https://github.com/kennylevinsen/wldash/issues/36

src/app.rs

@@ -99,6 +99,7 @@ impl AppInner {
             .unwrap();
 
         shell_surface.set_keyboard_interactivity(1);
+        shell_surface.set_size(1, 1);
         surface.set_buffer_scale(scale as i32);
         surface.commit();
         (surface, shell_surface)