MDL-61268 core: Fix empty string DB cehck

(amended by stronk7 to use the helper better)

lib/db/upgradelib.php

@@ -551,7 +551,7 @@ function upgrade_fix_block_instance_configuration() {
 
     $sql = "SELECT *
               FROM {block_instances}
-             WHERE configdata <> ''";
+             WHERE " . $DB->sql_isnotempty('block_instances', 'configdata', true, true);
     $blockinstances = $DB->get_recordset_sql($sql);
     foreach ($blockinstances as $blockinstance) {
         $configdata = base64_decode($blockinstance->configdata);

lib/tests/upgradelib_test.php

@@ -27,6 +27,7 @@ defined('MOODLE_INTERNAL') || die();
 
 global $CFG;
 require_once($CFG->libdir.'/upgradelib.php');
+require_once($CFG->libdir.'/db/upgradelib.php');
 
 /**
  * Tests various classes and functions in upgradelib.php library.