Fix handling EPUB noteref with nested elements (readium#503)

readium/navigator/src/main/java/org/readium/r2/navigator/R2BasicWebView.kt

@@ -287,7 +287,7 @@ internal open class R2BasicWebView(context: Context, attrs: AttributeSet) : WebV
  // We ignore taps on interactive element, unless it's an element we handle ourselves such as
  // pop-up footnotes.
  if (event.interactiveElement != null) {
- return handleFootnote(event.targetElement)
+ return handleFootnote(event.interactiveElement)
  }
 
  return runBlocking(uiScope.coroutineContext) { listener?.onTap(event.point) ?: false }