Do not perform double HTML-encoding

The content seems to be already HTML safe, e.g. for some feeds in UTF-8 with HTML special characters encoded, for some other feeds with all eligible characters HTML-encoded.
This problem was introduced in /dev when trying to address https://github.com/marienfressinaud/FreshRSS/issues/129
I think the patches for the UTF-8 bugs need to be applied first https://github.com/marienfressinaud/FreshRSS/pull/140
Tested with several feeds containing special characters, and seems fine.