Fix <h1> to be present even if title is "0"

Regression from 74b9803d9a, caused by a bug in LightNCandy which
caused {{foo}} to render "0", and {{#foo}} to pass as true with "0", but then
in {{#foo}}<b>{{foo}}</b>{{/foo} render as empty string producing "<b></b>".
In other words, the conditional is passing and the inner block is executed,
but the placeholder is mistakenly converting "0" => null => "" (empty string),
causing the <h1> to render but without any text in it.

Work around this bug by simply removing the conditional. Several other skins
already don't have this conditional and it's unclear why or in what
situation MediaWiki would send OutputPage to SkinTemplate without a title.

I think it would make sense in such rare case to still have a consistent
layout for extensions and gadgets to interact with and not omit the H1
element, but render it with the value that OutputPage gave it, even if it
is the empty string.

Bug: T219864
Change-Id: I6e04b512d2fe2e949ff5385cb38ceebe392fb255

includes/VectorTemplate.php

@@ -62,8 +62,9 @@ class VectorTemplate extends BaseTemplate {
 			'page-langcode' => $this->getSkin()->getTitle()->getPageViewLanguage()->getHtmlCode(),
 			'page-isarticle' => (bool)$this->data['isarticle'],
 
-			// Loose comparison with '!=' is intentional, to catch null and false too, but not '0'
-			'html-title' => ( $this->data['title'] != '' ? $this->get( 'title' ) : null ),
+			// Remember that the string '0' is a valid title.
+			// From OutputPage::getPageTitle, via ::setPageTitle().
+			'html-title' => $this->get( 'title', '' ),
 
 			'html-prebodyhtml' => $this->get( 'prebodyhtml', '' ),
 			'msg-tagline' => $this->getMsg( 'tagline' )->text(),

includes/templates/index.mustache

@@ -5,7 +5,7 @@
 	<a id="top"></a>
 	{{#html-sitenotice}}<div id="siteNotice" class="mw-body-content">{{{html-sitenotice}}}</div>{{/html-sitenotice}}
 	{{{html-indicators}}}
-	{{#html-title}}<h1 id="firstHeading" class="firstHeading" lang="{{page-langcode}}">{{{html-title}}}</h1>{{/html-title}}
+	<h1 id="firstHeading" class="firstHeading" lang="{{page-langcode}}">{{{html-title}}}</h1>
 	{{{html-prebodyhtml}}}
 	<div id="bodyContent" class="mw-body-content">
 		{{#page-isarticle}}<div id="siteSub" class="noprint">{{msg-tagline}}</div>{{/page-isarticle}}