Make sure we submit work even if we visited a camera. (#20595)

Alternative fix to #20318. We have existing code making sure that we do
work on a swapchain in `CameraDriverNode`. However, it's only protecting
against the case where we have no cameras spawned. We also need to check
that we actually did any rendering work, even if we have cameras in the
scene.

Tested on macOS.

Author: tychedelia

crates/bevy_render/src/render_graph/camera_driver_node.rs

@@ -63,7 +63,7 @@ impl Node for CameraDriverNode {
         // wgpu (and some backends) require doing work for swap chains if you call `get_current_texture()` and `present()`
         // This ensures that Bevy doesn't crash, even when there are no cameras (and therefore no work submitted).
         for (id, window) in world.resource::<ExtractedWindows>().iter() {
-            if camera_windows.contains(id) {
+            if camera_windows.contains(id) && render_context.has_commands() {
                 continue;
             }
 

crates/bevy_render/src/renderer/mod.rs

@@ -509,6 +509,10 @@ impl<'w> RenderContext<'w> {
         })
     }
 
+    pub(crate) fn has_commands(&mut self) -> bool {
+        self.command_encoder.is_some() || !self.command_buffer_queue.is_empty()
+    }
+
     /// Creates a new [`TrackedRenderPass`] for the context,
     /// configured using the provided `descriptor`.
     pub fn begin_tracked_render_pass<'a>(