Allow minimising in 2d (#4527)

# Objective

- We can't minimise if there's a 2d camera because ??? there legally must be a 2d target.
- Fixes https://github.com/bevyengine/bevy/issues/4526
- Fixes https://github.com/bevyengine/bevy/issues/4856

## Solution

- Make it not crash in those cases, just do nothing
- Seems to work ¯\\_(ツ)_/¯
- See also the companion commit in https://github.com/bevyengine/bevy/pull/3597 - 503c24717321bb2bb2681b358020ad1bcbef510e

Co-authored-by: Asteria <asteria131@outlook.com>

crates/bevy_core_pipeline/src/main_pass_2d.rs

@@ -39,10 +39,11 @@ impl Node for MainPass2dNode {
         world: &World,
     ) -> Result<(), NodeRunError> {
         let view_entity = graph.get_input_entity(Self::IN_VIEW)?;
-        let (transparent_phase, target) = self
-            .query
-            .get_manual(world, view_entity)
-            .expect("view entity should exist");
+        // If there is no view entity, do not try to process the render phase for the view
+        let (transparent_phase, target) = match self.query.get_manual(world, view_entity) {
+            Ok(it) => it,
+            _ => return Ok(()),
+        };
 
         if transparent_phase.items.is_empty() {
             return Ok(());

crates/bevy_ui/src/render/render_pass.rs

@@ -66,15 +66,16 @@ impl Node for UiPassNode {
         world: &World,
     ) -> Result<(), NodeRunError> {
         let view_entity = graph.get_input_entity(Self::IN_VIEW)?;
-        let (transparent_phase, target) = self
-            .query
-            .get_manual(world, view_entity)
-            .expect("view entity should exist");
+
+        // If there is no view entity, do not try to process the render phase for the view
+        let (transparent_phase, target) = match self.query.get_manual(world, view_entity) {
+            Ok(it) => it,
+            _ => return Ok(()),
+        };
 
         if transparent_phase.items.is_empty() {
             return Ok(());
         }
-
         let pass_descriptor = RenderPassDescriptor {
             label: Some("ui_pass"),
             color_attachments: &[RenderPassColorAttachment {