Update cpp/ql/lib/semmle/code/cpp/stmts/Stmt.qll

Author: jketema

cpp/ql/lib/semmle/code/cpp/stmts/Stmt.qll

@@ -456,7 +456,7 @@ class ConstevalOrNotConstevalIfStmt extends Stmt, @stmt_consteval_or_not_constev
    * ```
    * the result is the `BlockStmt` `{ return true; }`.
    */
-  Stmt getThen() { this.getChild(1) }
+  Stmt getThen() { result = this.getChild(1) }
 
   /**
    * Gets the 'else' statement of this '(not) constexpr if' statement, if any.