[ASTextNode] Ensure that isTruncated computes the correct value when sizing fast-path is used. (#2550) (#2763)

* Fix fast-path isTruncated.

* Clean up formatting; remove extra char.

AsyncDisplayKit/TextKit/ASTextKitRenderer.mm

@@ -261,6 +261,18 @@ static NSCharacterSet *_defaultAvoidTruncationCharacterSet()
   return lineCount;
 }
 
+- (BOOL)isTruncated
+{
+  if (self.canUseFastPath) {
+    CGRect boundedRect = [_attributes.attributedString boundingRectWithSize:CGSizeMake(_constrainedSize.width, CGFLOAT_MAX)
+                                                                    options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingTruncatesLastVisibleLine
+                                                                    context:nil];
+    return boundedRect.size.height > _constrainedSize.height;
+  } else {
+    return self.firstVisibleRange.length < _attributes.attributedString.length;
+  }
+}
+
 - (std::vector<NSRange>)visibleRanges
 {
   return _truncater.visibleRanges;