Porting #4182 to 2.5 email cloaking does not work with special char

Same patch merged in https://github.com/joomla/joomla-cms/pull/4182
Test: enter in an article as raw:
```
<p><a href="mailto:demo@demo.com"><span style="color: red;">Contattare l'associazione</span></a></p>
<div class="contact email"> </div>
<p><a href="mailto:demo@demo.com"><strong>Contattare l'associazione</strong></a></p>
<div class="contact email"> </div>
<div class="contact email"> </div>
<div class="contact email"> </div>
<div class="contact email"> ---------------------------------------</div>
<div class="contact email"><a href="mailto:info@testsite.com"><img style="margin: 0px 3px 0px 0px; float: left; width: 21px; height: 21px;" title="A nice title" src="images/powered_by.png" alt="A nice title" width="21" height="21" />info@testsite.com</a></div>
<div class="contact email"> </div>
<div>
<div class="contact email"><a href="mailto:info@testsite.com"><img src="images/powered_by.png" alt="" />info@testsite.com</a></div>
<div class="contact email"> </div>
<div>
<p>texte apres image</p>
</div>
<div class="contact email"><a href="mailto:info@testsite.com"><img style="margin: 0px 3px 0px 0px; float: left; width: 21px; height: 21px;" title="A nice title" src="images/powered_by.png" alt="A nice title" width="21" height="21" />texte'apresimage</a></div>
<div> </div>
<div class="contact email"><a href="mailto:info@testsite.com?subject= A text"><img style="margin: 0px 3px 0px 0px; float: left; width: 21px; height: 21px;" title="A nice title" src="images/powered_by.png" alt="A nice title" width="21" height="21" />texte'apresimage+ sujet</a></div>
<div>
<p>Testing with &lt;span something&gt;some text&lt;/span&gt;</p>
<p><a href="mailto:joe@nowhere.com"><span style="font-size: 18pt;">Joe_fontsize18</span></a></p>
<p><a href="mailto:joe@nowhere13.com?subject= A text"><span style="font-size: 14pt;">Joe'_subject_ fontsize13</span></a></p>
<p>Testing with &lt;span something&gt;email_adress&lt;/span&gt;</p>
<p><a href="mailto:joe@nowhere14.com"><span style="font-style: 14pt;">joe@nowhere14.com</span></a></p>
<p>Testing with (+subject)&lt;span something&gt;email_adress&lt;/span&gt;</p>
<p><a href="mailto:joe@nowhere16.com?subject= A text"><span style="font-size: 16pt;">joe@nowhere16.com</span></a></p>
<p><a href="mailto:joe@nowhere.com"><span style="color: red;">joe@nowhere.com</span></a></p>
<p>Uniquement strong</p>
<p><a href="mailto:joe@nowhere.com"><strong>something</strong></a></p>
<p>Uniquement strong avec subject et mail</p>
<p><a href="mailto:joe@nowhere.com?subject= A text"><strong>joe@nowhere.com</strong></a></p>
<p>strong+spansomething+text</p>
<p><a href="mailto:joe@nobody.com"><strong><span style="font-size: 9px;">Joe' Nobody</span></strong></a></p>
<p>strong+spansomething+mail</p>
<p><a href="mailto:joe@nobody.com"><strong><span style="font-size: 14px;">mymail@mysite.com</span></strong></a></p>
</div>
```
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