Prevent ImageBundles from causing constant layout recalculations (bev…

…yengine#1299)

Prevent ImageBundles from causing constant layout recalculations

crates/bevy_ui/src/widget/image.rs

@@ -27,10 +27,14 @@ pub fn image_node_system(
             .and_then(|material| material.texture.as_ref())
             .and_then(|texture_handle| textures.get(texture_handle))
         {
-            calculated_size.size = Size {
+            let size = Size {
                 width: texture.size.width as f32,
                 height: texture.size.height as f32,
             };
+            // Update only if size has changed to avoid needless layout calculations
+            if size != calculated_size.size {
+                calculated_size.size = size;
+            }
         }
     }
 }