Twenty Fifteen: a shorter header on small screens when there is no header text or header image looks more correct.

Props iamtakashi, fixes #30326.



Built from https://develop.svn.wordpress.org/trunk@30564


git-svn-id: http://core.svn.wordpress.org/trunk@30553 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: pinching to zoom in on landscape on iPads is breaking the layout with the sticky sidebar. Providing a one-column view on those screens looks good and will likely prevent other bugs we don't even know about.

Props iamtakashi, fixes #30366.



Built from https://develop.svn.wordpress.org/trunk@30565


git-svn-id: http://core.svn.wordpress.org/trunk@30554 1a063a9b-81f0-0310-95a4-ce76da25c4cd