avm1: Do not unwrap parent when removing objects pending removal

Turns out that sometimes objects pending removal do not have a parent.

I wasn't able to reproduce it, but it happens as we can see in error
reports.

Semantically this should be fine, as we mainly operate on the parent
here, but it's hard to be sure considering it's not reproducible.
It's better than panicking for sure.

core/src/avm1/runtime.rs

@@ -444,18 +444,20 @@ impl<'gc> Avm1<'gc> {
             Self::find_display_objects_pending_removal(root_clip, &mut out);
         }
 
-        for child in out {
+        for &child in &out {
             // Get the parent of this object
-            let parent = child.parent().unwrap();
-            let parent_container = parent.as_container().unwrap();
-
-            // Remove it
-            parent_container.remove_child_directly(context, child);
-
-            // Update pending removal state
-            parent_container
-                .raw_container_mut(context.gc())
-                .update_pending_removals();
+            if let Some(parent_container) = child.parent().and_then(|p| p.as_container()) {
+                // Remove it
+                parent_container.remove_child_directly(context, child);
+
+                // Update pending removal state
+                parent_container
+                    .raw_container_mut(context.gc())
+                    .update_pending_removals();
+            } else {
+                // TODO Investigate it. This situation seems impossible, yet it happens.
+                tracing::warn!("AVM1 object pending removal doesn't have a parent, object={:?}, pending removal={:?}", child, out);
+            }
         }
     }