make viewer work for files_sp, by resetting entryList and pageList for any new directory load

internal/js/files_support.js

@@ -471,6 +471,9 @@ function getDirEntries(dir_id, back)
         dataType: 'json', // Expect JSON response
         success: function(res) {
             document.entries=res
+            // rebuild entryList/pageList as each dir comes with new entries
+            entryList=res.map(obj => obj.id);
+            pageList=entryList.slice(0, OPT.howMany)
             if( back )
                 document.back_id = res[0].in_dir.eid
             drawPageOfFigures()