core: Avoid panic when display objects are manipulated in clearly invalid ways.

core/src/display_object.rs

@@ -528,7 +528,7 @@ pub trait TDisplayObject<'gc>:
     /// Returned by the ActionScript `_width`/`width` properties.
     fn width(&self) -> f64 {
         let bounds = self.local_bounds();
-        (bounds.x_max - bounds.x_min).to_pixels()
+        (bounds.x_max.saturating_sub(bounds.x_min)).to_pixels()
     }
 
     /// Sets the pixel width of this display object in local space.
@@ -567,7 +567,7 @@ pub trait TDisplayObject<'gc>:
     /// Returned by the ActionScript `_height`/`height` properties.
     fn height(&self) -> f64 {
         let bounds = self.local_bounds();
-        (bounds.y_max - bounds.y_min).to_pixels()
+        (bounds.y_max.saturating_sub(bounds.y_min)).to_pixels()
     }
     /// Sets the pixel height of this display object in local space.
     /// Set by the ActionScript `_height`/`height` properties.

swf/src/types.rs

@@ -95,6 +95,10 @@ impl Twips {
     pub fn to_pixels(self) -> f64 {
         f64::from(self.0) / Self::TWIPS_PER_PIXEL
     }
+
+    pub fn saturating_sub(self, rhs: Self) -> Self {
+        Self(self.0.saturating_sub(rhs.0))
+    }
 }
 
 impl std::ops::Add for Twips {