js prototype popupTemplate prepends 'undefined'

Because line 1162 doesn't default the template variable,
var template;

the next line with a += uses the string value 'undefined' to start the template.

It isn't apparently causing any issues, as jQuery seems to know to throw it out before instantiating the object, but it was something I came across whilst debugging an extra trailing "

" issue in my code.

Line 1162 should default to an empty string.
var template = '';

Ludicrously tiny patch included.