pkp/pkp-lib#11396 Make OPS more resilient to missing theme plugins

Author: asmecher

templates/frontend/objects/preprint_details.tpl

@@ -199,8 +199,8 @@
 
 			{call_hook name="Templates::Preprint::Main"}
 
-			{* Usage statistics chart*}
-			{if $activeTheme->getOption('displayStats') != 'none'}
+			{* Usage statistics chart *}
+			{if $activeTheme && $activeTheme->getOption('displayStats') != 'none'}
 				{$activeTheme->displayUsageStatsGraph($preprint->getId())}
 				<section class="item downloads_chart">
 					<h2 class="label">

templates/frontend/pages/indexServer.tpl

@@ -27,7 +27,7 @@
 		{include file="frontend/components/highlights.tpl" highlights=$highlights}
 	{/if}
 
-	{if !$activeTheme->getOption('useHomepageImageAsHeader') && $homepageImage}
+	{if $activeTheme && !$activeTheme->getOption('useHomepageImageAsHeader') && $homepageImage}
 		<img src="{$publicFilesDir}/{$homepageImage.uploadName|escape:"url"}" alt="{$homepageImageAltText|escape}">
 	{/if}
 
@@ -47,7 +47,7 @@
 	</section>
 
 	{* Server Description *}
-	{if $activeTheme->getOption('showDescriptionInServerIndex')}
+	{if $activeTheme && $activeTheme->getOption('showDescriptionInServerIndex')}
 		<section class="homepage_about">
 			<a id="homepageAbout"></a>
 			<h2>{translate key="about.aboutContext"}</h2>