properly update bind group ids when setting dynamic bindings. (#560)

crates/bevy_render/src/pipeline/pipeline.rs

@@ -152,6 +152,7 @@ impl PipelineDescriptor {
         if !dynamic_bindings.is_empty() {
             // set binding uniforms to dynamic if render resource bindings use dynamic
             for bind_group in layout.bind_groups.iter_mut() {
+                let mut binding_changed = false;
                 for binding in bind_group.bindings.iter_mut() {
                     let current = DynamicBinding {
                         bind_group: bind_group.index,
@@ -164,9 +165,14 @@ impl PipelineDescriptor {
                         } = binding.bind_type
                         {
                             *dynamic = true;
+                            binding_changed = true;
                         }
                     }
                 }
+
+                if binding_changed {
+                    bind_group.update_id();
+                }
             }
         }