Update extension_edit.php

Prevent a SQL error when adding a new user.

app/extensions/extension_edit.php

@@ -688,6 +688,7 @@
 	unset($sql, $prep_statement);
 
 //get assigned users
+	if (is_uuid($extension_uuid)) {
 		$sql = "SELECT u.username, e.user_uuid FROM v_extension_users as e, v_users as u ";
 		$sql .= "where e.user_uuid = u.user_uuid  ";
 		$sql .= "and u.user_enabled = 'true' ";
@@ -701,6 +702,7 @@
 			$assigned_user_uuids[] = $field['user_uuid'];
 		}
 		unset($sql, $prep_statement);
+	}
 
 //get the users
 	$sql = "SELECT * FROM v_users ";