Fix series selection for SBP FO stylesheets

Use the same algorithm as in HTML.

Ref: DOCTEAM-1368
Ref: PR #625

sbp/fo/article.titlepage.templates.xsl

@@ -37,7 +37,14 @@
         </fo:table-cell>
         <fo:table-cell text-align="right" color="&c_jungle;">
           <fo:block font-size="&xxx-large;pt">
-            <xsl:value-of select="$json-ld-seriesname"/>
+            <xsl:choose>
+              <xsl:when test="$json-ld-seriesname != ''">
+                <xsl:value-of select="$json-ld-seriesname"/>
+              </xsl:when>
+              <xsl:otherwise>
+                <xsl:apply-templates select="d:info/d:meta[@name='series'][1]" mode="article.titlepage.recto.auto.mode"/>
+              </xsl:otherwise>
+            </xsl:choose>
           </fo:block>
           <fo:block font-size="&large;pt" space-before="1em">
             <xsl:apply-templates select="d:info/d:meta[@name='category'][1]" mode="article.titlepage.recto.auto.mode"/>
@@ -107,7 +114,8 @@
   </xsl:template>
 
   <xsl:template match="d:meta[@name='series']" mode="article.titlepage.recto.auto.mode">
-    <!-- We don't process it anymore, using $json-ld-seriesname parameter -->
+    <!-- Only process it when $json-ld-seriesname != '' -->
+    <xsl:apply-templates/>
   </xsl:template>
 
   <xsl:template match="d:meta[@name='category']" mode="article.titlepage.recto.auto.mode">

sbp/xhtml/titlepage.templates.xsl

@@ -267,7 +267,7 @@
     </xsl:choose>
 
     <div class="series-category">
-      <xsl:comment/>
+      <xsl:comment/><!-- Add empty comment in case we don't create series nor categories -->
       <xsl:call-template name="add.series.name"/>
       <xsl:apply-templates mode="article.titlepage.recto.auto.mode" select="d:info/d:meta[@name='category' or @name='type']"/>
     </div>