Response post processing shouldn't happen if the content type isn't HTML

[espen42]

It appears some (or all?) responses where body and contentType are javascript are still postprocessed. This causes an error for some JS (but not all), see starter-nextjs #81

[espen42]

@rymsha

[rymsha]

Error is caused by incompatibility to parse the response as HTML
site mapping controller post-processor does not take into account that the response may be not HTML.

The workaround is to use postProcess : false in response

Caused by: com.enonic.xp.portal.impl.rendering.RenderException: Failed to post process document
	at com.enonic.xp.portal.impl.parser.HtmlBlockParser.parse(HtmlBlockParser.java:41)
	at com.enonic.xp.portal.impl.postprocess.PostProcessEvaluator.evaluateInstructions(PostProcessEvaluator.java:55)
	at com.enonic.xp.portal.impl.postprocess.PostProcessorImpl.processResponseInstructions(PostProcessorImpl.java:67)
	at com.enonic.xp.portal.impl.rendering.PostProcessingRenderer.render(PostProcessingRenderer.java:26)
	at com.enonic.xp.portal.impl.rendering.RendererDelegateImpl.lambda$render$1(RendererDelegateImpl.java:40)
	at java.base/java.util.Optional.map(Optional.java:265)
	at com.enonic.xp.portal.impl.rendering.RendererDelegateImpl.render(RendererDelegateImpl.java:40)
	at com.enonic.xp.portal.impl.handler.mapping.MappingHandlerWorker.renderController(MappingHandlerWorker.java:70)
	at com.enonic.xp.portal.impl.handler.mapping.MappingHandlerWorker.execute(MappingHandlerWorker.java:54)
	at com.enonic.xp.portal.impl.handler.mapping.MappingHandler.handleController(MappingHandler.java:95)
	at com.enonic.xp.portal.impl.handler.mapping.MappingHandler.doHandle(MappingHandler.java:69)
	at com.enonic.xp.portal.impl.handler.mapping.MappingHandler.doHandle(MappingHandler.java:24)
	at com.enonic.xp.web.handler.BaseWebHandler.handle(BaseWebHandler.java:66)
	at com.enonic.xp.web.impl.handler.WebHandlerChainImpl.handle(WebHandlerChainImpl.java:30)
	at com.enonic.xp.web.handler.BaseWebHandler.handle(BaseWebHandler.java:75)
	at com.enonic.xp.web.impl.handler.WebHandlerChainImpl.handle(WebHandlerChainImpl.java:30)
	at com.enonic.xp.web.handler.BaseWebHandler.handle(BaseWebHandler.java:75)
	at com.enonic.xp.web.impl.handler.WebHandlerChainImpl.handle(WebHandlerChainImpl.java:30)
	at com.enonic.xp.portal.handler.BasePortalHandler.doHandle(BasePortalHandler.java:46)
	... 111 common frames omitted

Simple JS is just more-ore-less valid HTML and can be "processed", others are too complex for html parser.
There is no reason to do that for non-html responses., So fix is to disable post-processing for non-html responses.