Correctly handle zero-frame MovieClip

A MovieClip with zero frames can still have a child added
through ActionScript, which ticks normally.

core/src/display_object/movie_clip.rs

@@ -2650,7 +2650,9 @@ impl<'gc> TDisplayObject<'gc> for MovieClip<'gc> {
     fn construct_frame(&self, context: &mut UpdateContext<'_, 'gc>) {
         // AVM1 code expects to execute in line with timeline instructions, so
         // it's exempted from frame construction.
-        if self.movie().is_action_script_3() && self.frames_loaded() >= 1 {
+        if self.movie().is_action_script_3()
+            && (self.frames_loaded() >= 1 || self.total_frames() == 0)
+        {
             let is_load_frame = !self.0.read().initialized();
             let needs_construction = if matches!(self.object2(), Avm2Value::Null) {
                 self.allocate_as_avm2_object(context, (*self).into());

tests/tests/swfs/avm2/zero_frame_clip/Main.as

@@ -0,0 +1,17 @@
+package  {
+	
+	import flash.display.MovieClip;
+
+	
+	
+	public class Main extends MovieClip {
+		
+		
+		public function Main() {
+			var child = MovieClip(this.getChildAt(0));
+			trace("Child: " + child + " totalFrames: " + child.totalFrames);
+			child.addChild(new NormalChild());
+		}
+	}
+	
+}

tests/tests/swfs/avm2/zero_frame_clip/TraceConstructor.as

@@ -0,0 +1,14 @@
+package  {
+	
+	import flash.display.MovieClip;
+	
+	
+	public class TraceConstructor extends MovieClip {
+		
+		
+		public function TraceConstructor() {
+			trace("Constructed TraceConstructor with name: " + this.name);
+		}
+	}
+	
+}

tests/tests/swfs/avm2/zero_frame_clip/output.txt

@@ -0,0 +1,3 @@
+Child: [object ZeroFrames] totalFrames: 0
+Constructed TraceConstructor with name: child1
+Constructed TraceConstructor with name: child2

tests/tests/swfs/avm2/zero_frame_clip/test.toml

@@ -0,0 +1,3 @@
+# NOTE - test.swf was manually edited to remove the single (empty) frame,
+# so that it actually has zero frames.
+num_ticks = 3