Hide download button only w/o photos and subalbums.

Previously, an album with subalbums, but without photos, was hiding
the download button.

src/scripts/header.js

@@ -141,8 +141,8 @@ header.setMode = function(mode) {
 			header.dom('.header__toolbar--album').addClass('header__toolbar--visible')
 
 			// Hide download button when album empty
-			if (album.json.content===false) $('#button_archive').hide()
-			else                            $('#button_archive').show()
+			if (album.json.content===false && album.subjson.num==0) $('#button_archive').hide()
+			else                                                    $('#button_archive').show()
 
 			// Hide download button when not logged in and album not downloadable
 			if (lychee.publicMode===true && album.json.downloadable==='0') $('#button_archive').hide()