render: only attempt to create camera bind group when the camera bind group descriptor exists

this fixes panics in empty scenes

crates/bevy_render/src/render_graph/nodes/pass_node.rs

@@ -135,12 +135,16 @@ impl Node for PassNode {
                 } else {
                     continue;
                 };
-
+            if render_context
-            let camera_bind_group = BindGroup::build().add_binding(0, camera_binding).finish();
-            render_context
                 .resources()
-                .create_bind_group(self.camera_bind_group_descriptor.id, &camera_bind_group);
+                .bind_group_descriptor_exists(self.camera_bind_group_descriptor.id)
-            camera_info.bind_group_id = Some(camera_bind_group.id);
+            {
+                let camera_bind_group = BindGroup::build().add_binding(0, camera_binding).finish();
+                render_context
+                    .resources()
+                    .create_bind_group(self.camera_bind_group_descriptor.id, &camera_bind_group);
+                camera_info.bind_group_id = Some(camera_bind_group.id);
+            }
         }
 
         render_context.begin_pass(

crates/bevy_render/src/renderer/headless_render_resource_context.rs

@@ -120,4 +120,8 @@ impl RenderResourceContext for HeadlessRenderResourceContext {
     fn get_buffer_info(&self, buffer: BufferId) -> Option<BufferInfo> {
         self.buffer_info.read().unwrap().get(&buffer).cloned()
     }
+    fn bind_group_descriptor_exists(&self, _bind_group_descriptor_id: BindGroupDescriptorId)
+        -> bool {
+        false
+    }
 }

crates/bevy_render/src/renderer/render_resource_context.rs

@@ -48,6 +48,8 @@ pub trait RenderResourceContext: Downcast + Send + Sync + 'static {
         pipeline_descriptor: &PipelineDescriptor,
         shaders: &Assets<Shader>,
     );
+    fn bind_group_descriptor_exists(&self, bind_group_descriptor_id: BindGroupDescriptorId)
+        -> bool;
     fn create_bind_group(
         &self,
         bind_group_descriptor_id: BindGroupDescriptorId,

crates/bevy_wgpu/src/renderer/wgpu_render_resource_context.rs

@@ -433,6 +433,14 @@ impl RenderResourceContext for WgpuRenderResourceContext {
         render_pipelines.insert(pipeline_handle, render_pipeline);
     }
 
+    fn bind_group_descriptor_exists(
+        &self,
+        bind_group_descriptor_id: BindGroupDescriptorId,
+    ) -> bool {
+        let bind_group_layouts = self.resources.bind_group_layouts.read().unwrap();
+        bind_group_layouts.get(&bind_group_descriptor_id).is_some()
+    }
+
     fn create_bind_group(
         &self,
         bind_group_descriptor_id: BindGroupDescriptorId,