Optional vlsuite layout regions are rendered twice

Problem/Motivation

Currently, the optional regions of the layouts from the vlsuite_layout module are being rendered twice in their twig templates: one to check the layout has content, another one to render it.

This may produce unexpected bugs as duplicated form submissions (this problem has happened in projects using webform). Also, content should be rendered once as is only printed once. Consequently, it improves the performance as fewer renders are done.

Steps to reproduce

Use any layout from vlsuite layout module.

Proposed resolution

Instead of rendering twice, store the rendered content in a variable and use it for both cases.