refs https://github.com/TryGhost/Team/issues/41
- if you add invalid handlebars logic e.g. {{if condition condition}}, handlebars throws an error
- in case of having invalid hbs in an amp page, the amp component throwed another syntax error (which is fixed in this PR)
- furthermore the `setTemplate` helper function had a logic bug, which did not handle errors correctly
- if there is an error and a template is set (e.g. amp), we have to still render the error page and not the amp page
- this fix only ensures that the error handling is correct, we still see the error of the "ugly" handlebars message
- e.g. [amp.hbs] Cannot read property 'includeZero' of undefined
- but no longer -> Cannot read property 'html' of undefined (which was a syntax error in Ghost)
d87fbeca49