fixes #698 change condition to add meta tag

we only want the meta tag when the exif data is displayed using the url parameter, this avoids the no index no follow for some themes that force displaying metadata

picture.php

@@ -606,7 +606,7 @@ $metadata_showable = trigger_change(
   $picture['current']
   );
 
-if ( $metadata_showable and pwg_get_session_var('show_metadata') )
+if ( isset($_GET['metadata']) )
 {
   $page['meta_robots']=array('noindex'=>1, 'nofollow'=>1);
 }
@@ -676,12 +676,10 @@ SELECT *
       
       $format['filesize'] = sprintf('%.1fMB', $format['filesize']/1024);
     }
-
     $template->append('current', array('formats' => $formats), true);
   }
 }
 
-
 if ($page['slideshow'])
 {
   $tpl_slideshow = array();