iris: retain next-frame staging allocation

iris/core/src/ui/render_state.rs

@@ -285,12 +285,14 @@ impl UiRenderState {
         self.apply_free();
         #[cfg(debug_assertions)]
         debug_assert!(self.primitive_counts_agree(), "{}", self.orphan_report(rsc),);
-        let next: Vec<_> = std::mem::take(&mut self.next_frame)
-            .into_iter()
-            .filter(|id| self.active.contains_key(id))
-            .collect();
-        let requested = !next.is_empty();
-        rsc.widgets_mut().needs_redraw.extend(next);
+        let active = &self.active;
+        let mut requested = false;
+        for id in self.next_frame.drain() {
+            if active.contains_key(&id) {
+                rsc.widgets_mut().needs_redraw.insert(id);
+                requested = true;
+            }
+        }
         requested
     }