Fix rendering outside a web request in non TEST env (#60)

[billgonemad]

Fixes #60

Problem

Since 364bd4e, RenderEnvironment only bound a web request in the TEST environment. In production/development, rendering off-request (jobs, async tasks, BootStrap) NPE'd as soon as a template used a taglib.

Fix

• No request bound: binds a GrailsWebRequest over Grails' servlet-free PageRenderer stubs (the same ones groovyPageRenderer uses). It uses the real context path and runs request-scoped cleanup.
• Request already bound: reuses the caller's request, so session, flash, params and request attributes keep working. Only out, the locale resolver and WrappedResponseHolder are swapped, and they are restored afterwards.
• The caller's request state is always restored, including on exceptions and nested renders.

Behaviour change

Off-request, session, without grails.serverURLthrow UnsupportedOperationExceptionin all environments. They already NPE'd in production on 7.0.x, but in TEST they used to work, so downstream test suites may notice. Setgrails.serverURL`.

Testing

New integration specs force grails.env=production, since TEST hid the bug. 14 of the 18 new tests fail against 7.0.x. ./gradlew check build docs :example:integrationTest: 90 tests, 0 failures.

[sbglasius]

Minor suggestion on RenderEnvironment.with(...): env.init() runs outside the try/finally. init() binds the render request via RequestContextHolder.setRequestAttributes(...) and then sets request attributes and WrappedResponseHolder. If a later step throws, close() never runs, so the mock request stays bound on the thread and the caller state is not restored. That matters on pooled job threads.

Suggestion: make init() safe on partial failure. For example, wrap the body after the binding in a try/catch that calls restoreCallerState() and rethrows, or move env.init() inside the try. If you do the latter, make close() tolerate renderRequestAttributes == null, because init() can fail before it is assigned.

[billgonemad]

@sbglasius Thanks for the review. Went with moving env.init() inside of the try block and updating the close()

[sbglasius]

Re-reviewed 1462b37: init() failure is now handled (init inside try, close() tolerates unset render request). LGTM.

[sbglasius]

@billgonemad Thank you for your contribution. The release is running and the artifact should be available as version 7.0.2 in the next hour or so.