Include a title block if a subtitle is present

Fixes #4764

Author: dragonstyle

src/resources/formats/html/pandoc/template.html

@@ -34,6 +34,8 @@
 
 $if(title)$
 $title-block.html()$
+$elseif(subtitle)$
+$title-block.html()$
 $endif$
 
 $if(toc)$

src/resources/formats/html/pandoc/title-block.html

@@ -1,8 +1,7 @@
 <header id="title-block-header">
-<h1 class="title">$title$</h1>
+$if(title)$<h1 class="title">$title$</h1>$endif$
 $if(subtitle)$
 <p class="subtitle">$subtitle$</p>
-
 $endif$
 $for(author)$
 <p class="author">$author$</p>

src/resources/formats/html/templates/banner/title-block.html

@@ -2,7 +2,7 @@
 <header id="title-block-header" class="quarto-title-block default$if(quarto-template-params.banner-header-class)$ $quarto-template-params.banner-header-class$$endif$">
   <div class="quarto-title-banner">
     <div class="quarto-title column-body">
-      <h1 class="title">$title$</h1>
+      $if(title)$<h1 class="title">$title$</h1>$endif$
       $if(subtitle)$
       <p class="subtitle lead">$subtitle$</p>
       $endif$