title: NSMutableAttributedString's attribute NSStrikethroughStyleAttributeName doesn't work correctly in iOS8
body: <p>I have a mutable attributed string without NSStrikethroughStyleAttributeName attribute like this:</p>
  
  <pre><code>NSMutableAttributedString *str1 = [[NSMutableAttributedString alloc] initWithString:@"aaaa" attributes:@{NSStrikethroughStyleAttributeName:[NSNumber numberWithInteger:NSUnderlineStyleSingle]}];
  </code></pre>
  
  <p>and another mutable attributed string with NSStrikethroughStyleAttributeName attribute like this:</p>
  
  <pre><code>NSMutableAttributedString *str2 = [[NSMutableAttributedString alloc] initWithString:@"bbbb"];
  </code></pre>
  
  <p>and a whole string containing two strings above:</p>
  
  <pre><code>NSMutableAttributedString *labelString = [[NSMutableAttributedString alloc] init];
  [labelString appendAttributedString:str1];
  [labelString appendAttributedString:str2];
  </code></pre>
  
  <p>when I attach the whole string to a UILabel:</p>
  
  <pre><code>_label.attributedText = labelString;
  </code></pre>
  
  <p>It both display well in iOS7 and iOS8, like this:</p>
  
  <p><del>aaaa</del>bbbb</p>
  
  <p>But when I exchange their positions:</p>
  
  <pre><code>[labelString appendAttributedString:str2];
  [labelString appendAttributedString:str1];
  </code></pre>
  
  <p>It display correctly in iOS7 but not correctly in iOS8</p>
  
  <p>ios7:  bbbb<del>aaaa</del>          ios8: bbbbaaaa</p>
  
  <p>It seems that in iOS8, UILabel doesn't render the strikethrough correctly if the first character in the attributed string is not strikethroughed.
  I think this is a bug in iOS8, is there anyone who encounter the same problem with me?</p>