Backport: email cloaking does not work with & in text to 2.5.x

Please see the orginal issue for 3.x (https://github.com/joomla/joomla-cms/issues/4263) and the PR against staging (https://github.com/joomla/joomla-cms/pull/4273)

The same issue is in 2.5.x and the same fix work good for me.

As the code is by @heleneross i mark my test as the first successful test. The PR against staging was by @n9iels Thank you guys.