Use empty buffer as stand in for empty array buffers

With a fallback "empty" binding, we no longer have to send junk point
light and occluder data to the GPU (which I believe has been causing
some issues).

src/render/extract.rs

@@ -46,17 +46,6 @@ pub fn extract_point_lights(
             cast_shadows: if point_light.cast_shadows { 1 } else { 0 },
         });
     }
-
-    // BufferVec won't write to the GPU if there aren't any point lights.
-    // For now we can spawn an empty point light to get around this.
-    commands.spawn(ExtractedPointLight2d {
-        transform: Vec2::ZERO,
-        intensity: 0.0,
-        radius: 0.0,
-        falloff: 0.0,
-        color: LinearRgba::BLACK,
-        cast_shadows: 0,
-    });
 }
 
 pub fn extract_light_occluders(
@@ -79,10 +68,6 @@ pub fn extract_light_occluders(
 
         commands.get_or_spawn(entity).insert(extracted_occluder);
     }
-
-    // BufferVec won't write to the GPU if there aren't any point lights.
-    // For now we can spawn an empty occluder to get around this.
-    commands.spawn(ExtractedLightOccluder2d::default());
 }
 
 pub fn extract_ambient_lights(

src/render/light_map/node.rs

@@ -11,6 +11,7 @@ use bevy::render::renderer::RenderDevice;
 use bevy::render::view::{ViewUniformOffset, ViewUniforms};
 use smallvec::{smallvec, SmallVec};
 
+use crate::render::empty_buffer::EmptyBuffer;
 use crate::render::extract::{ExtractedAmbientLight2d, ExtractedPointLight2d};
 use crate::render::sdf::SdfTexture;
 
@@ -58,7 +59,8 @@ impl ViewNode for LightMapNode {
                 .binding(),
             world
                 .resource::<GpuArrayBuffer<ExtractedPointLight2d>>()
-                .binding(),
+                .binding()
+                .or(world.resource::<EmptyBuffer>().binding()),
             world.resource::<PointLightMetaBuffer>().buffer.binding(),
         )
         else {

src/render/sdf/node.rs

@@ -10,6 +10,7 @@ use bevy::render::renderer::RenderDevice;
 use bevy::render::view::{ViewUniformOffset, ViewUniforms};
 use smallvec::{smallvec, SmallVec};
 
+use crate::render::empty_buffer::EmptyBuffer;
 use crate::render::extract::ExtractedLightOccluder2d;
 
 use super::pipeline::SdfPipeline;
@@ -39,7 +40,8 @@ impl ViewNode for SdfNode {
             world.resource::<ViewUniforms>().uniforms.binding(),
             world
                 .resource::<GpuArrayBuffer<ExtractedLightOccluder2d>>()
-                .binding(),
+                .binding()
+                .or(world.resource::<EmptyBuffer>().binding()),
         ) else {
             return Ok(());
         };