[search] avoid errors when a filter returns no item

include/functions_search.inc.php

@@ -159,7 +159,7 @@ function get_sql_search_clause($search)
     // ((field1 LIKE '%word1%' OR field2 LIKE '%word1%')
     // AND (field1 LIKE '%word2%' OR field2 LIKE '%word2%'))
     $word_clauses = array();
-    $cat_ids_by_word = array();
+    $cat_ids_by_word = $tag_ids_by_word = array();
     foreach ($search['fields']['allwords']['words'] as $word)
     {
       $field_clauses = array();

index.php

@@ -367,11 +367,11 @@ SELECT
   ORDER BY counter DESC
 ;';
       $added_by = query2array($query);
+      $user_ids = array();
 
       if (count($added_by) > 0)
       {
         // now let's find the usernames of added_by users
-        $user_ids = array();
         foreach ($added_by as $i)
         {
           $user_ids[] = $i['added_by_id'];