core: Fix panic on unsetting self-referential masker

core/src/display_object.rs

@@ -1666,7 +1666,8 @@ pub trait TDisplayObject<'gc>:
         remove_old_link: bool,
     ) {
         if remove_old_link {
-            if let Some(old_masker) = self.base().masker() {
+            let old_masker = self.base().masker();
+            if let Some(old_masker) = old_masker {
                 old_masker.set_maskee(gc_context, None, false);
             }
             if let Some(parent) = self.parent() {
@@ -1686,7 +1687,8 @@ pub trait TDisplayObject<'gc>:
         remove_old_link: bool,
     ) {
         if remove_old_link {
-            if let Some(old_maskee) = self.base().maskee() {
+            let old_maskee = self.base().maskee();
+            if let Some(old_maskee) = old_maskee {
                 old_maskee.set_masker(gc_context, None, false);
             }
             self.invalidate_cached_bitmap(gc_context);

tests/tests/swfs/avm2/displayobject_mask_self_referential/Test.as

@@ -0,0 +1,14 @@
+// compiled with mxmlc
+
+
+package {
+    import flash.display.MovieClip;
+
+    public class Test extends MovieClip {
+        public function Test(){
+            var mc = new MovieClip();
+            this.mask = this;
+            this.mask = mc;
+        }
+    }
+}

tests/tests/swfs/avm2/displayobject_mask_self_referential/test.toml

@@ -0,0 +1,3 @@
+# tests a probable (no access to original repro) cause of
+# https://github.com/ruffle-rs/ruffle/issues/14747
+num_frames = 1