Bug 1096513 - Fix build error on a CLOSED TREE. r=me

gfx/layers/apz/src/Axis.cpp

@@ -195,7 +195,7 @@ ParentLayerCoord Axis::GetOverscroll() const {
   ParentLayerCoord result = (mOverscroll - mOverscrollOffset) / mOverscrollScale;
 
   // Assert that we return overscroll in the correct direction
-  MOZ_ASSERT((result * mOverscrollOffset) >= 0.0f);
+  MOZ_ASSERT((result.value * mOverscrollOffset.value) >= 0.0f);
 
   return result;
 }