Make index not unique (#537)

The reason for this is because there may be plans
to extend this plugin to allow for multiple
certificate issues.

Also, there was a bug that allowed for duplicate
issues which was resolved but those issues could
still exist in user's databases. Instead of creating
an upgrade path to delete them just leave it for now.

db/install.xml

@@ -55,7 +55,7 @@
         <KEY NAME="customcert" TYPE="foreign" FIELDS="customcertid" REFTABLE="customcert" REFFIELDS="id"/>
       </KEYS>
       <INDEXES>
-        <INDEX NAME="userid-customcertid" UNIQUE="true" FIELDS="userid, customcertid"/>
+        <INDEX NAME="userid-customcertid" UNIQUE="false" FIELDS="userid, customcertid"/>
       </INDEXES>
     </TABLE>
     <TABLE NAME="customcert_pages" COMMENT="Stores each page of a custom cert">

db/upgrade.php

@@ -203,7 +203,7 @@ function xmldb_customcert_upgrade($oldversion) {
     if ($oldversion < 2023042403) {
         // Define index to be added to customcert_issues.
         $table = new xmldb_table('customcert_issues');
-        $index = new xmldb_index('userid-customcertid', XMLDB_INDEX_UNIQUE, ['userid', 'customcertid']);
+        $index = new xmldb_index('userid-customcertid', XMLDB_INDEX_NOTUNIQUE, ['userid', 'customcertid']);
 
         // Conditionally launch add index.
         if (!$dbman->index_exists($table, $index)) {