TemplateViewHelper - Exception when used in context without request

[haraldglaser]

This patch in merged pull request "Assign resolved Request in TemplateViewHelper #1907" leads to an error if the template containing the viewhelper does not contain the necessary information for RequestResolver::resolveRequestFromRenderingContext to resolve a request.

I think it's a legitimate use to include this viewhelper in a template which itself has no request attached. In this case in my opinion it shouldn't throw an error but proceed without setting a request on the targeted view.

My actual usecase: this viewhelper is part of a custom backend preview (https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/ApiOverview/ContentElements/CustomBackendPreview.html#ConfigureCE-Preview-PageTSconfig). As this feature uses a StandaloneView without further configuration, there is no easy way to use partials (at least none I am aware of). Prior to the change in the pull request it was possible to use the TemplateViewHelper to "simulate" partials.
This now fails with message "Unable to resolve request from RenderingContext" thrown in RequestResolver::resolveRequestFromRenderingContext.