The 'cpage' query var is only set when using `comments_template()` to display
comments. If displaying them in a context where 'cpage' is not yet set, the
default value should be 1, not 0.
Props MomDad, couturefreak.
Fixes#20319.
git-svn-id: https://develop.svn.wordpress.org/trunk@31617 602fd350-edb4-49c9-b593-d223f7449a82
