Bug with img alt="" parsing inside p-*

[gRegorLove]

This if-elseif-condition should check hasAttribute('alt') and allow empty values rather than skipping if the alt is empty.

Reference:
http://pin13.net/mf2/?url=http%3A%2F%2Fmention-tech.appspot.com%2Ftesting.html "mention.tech" appended to end of 'org' and 'name'
https://indiewebcamp.com/irc/2016-04-12#t1460485540966

[gRegorLove]

Fixed with #90.