avm1: Support loading into _level in GetURL2

Calling loadMovieNum with a variable parameter compiles into a
GetURL2 call with a `_level` window target parameter. Previously
this triggered Ruffle to try to navigate to the SWF. Now it
properly loads the SWF inside the current movie.

core/src/avm1/activation.rs

@@ -1340,6 +1340,29 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
                 context.navigator.spawn_future(process);
             }
 
+            return Ok(FrameControl::Continue);
+        } else if window_target.starts_with("_level") && url.len() > 6 {
+            // target of `_level#` indicates a `loadMovieNum` call.
+            match window_target[6..].parse::<u32>() {
+                Ok(level_id) => {
+                    let fetch = context.navigator.fetch(&url, RequestOptions::get());
+                    let level = self.resolve_level(level_id, context);
+
+                    let process = context.load_manager.load_movie_into_clip(
+                        context.player.clone().unwrap(),
+                        level,
+                        fetch,
+                        None,
+                    );
+                    context.navigator.spawn_future(process);
+                }
+                Err(e) => log::warn!(
+                    "Couldn't parse level id {} for action_get_url_2: {}",
+                    url,
+                    e
+                ),
+            }
+
             return Ok(FrameControl::Continue);
         } else {
             let vars = match NavigationMethod::from_send_vars_method(swf_method) {
@@ -1353,7 +1376,6 @@ impl<'a, 'gc: 'a> Activation<'a, 'gc> {
                 vars,
             );
         }
-
         Ok(FrameControl::Continue)
     }
 

core/tests/swfs/avm1/loadmovienum/output.txt

@@ -1,2 +1,3 @@
-Loading movie
+Loading movies
+Child movie loaded!
 Child movie loaded!