Move initial captcha src to constructor
Move initial captcha src to constructor

Rather than causing a state refresh, if we already have a captcha iden,
build the source url in the constructor.

curioussavage/reddit-mobile,uzi/reddit-mobile,madbook/reddit-mobile,uzi/reddit-mobile,madbook/reddit-mobile,DogPawHat/reddit-mobile,DogPawHat/reddit-mobile,uzi/reddit-mobile,curioussavage/reddit-mobile,madbook/reddit-mobile