adjust migration to prevent errors (adjusts fe081811), re #736

db/migrations/20220401_add_index_to_cw_user_progresses_v50.php

@@ -8,6 +8,14 @@ final class AddIndexToCwUserProgressesV50 extends Migration
 
     public function up()
     {
+        // avoid running this migration twice
+        $query = "SHOW INDEX FROM `cw_user_progresses` WHERE Key_name = 'block_id'";
+        $result = DBManager::get()->query($query);
+
+        if ($result && $result->rowCount() > 0) {
+            return;
+        }
+
         $query = "ALTER TABLE `cw_user_progresses`
                   ADD INDEX `block_id` (`block_id`)";
         DBManager::get()->exec($query);