Improve "pages/ not found error"

[rauchg]

Right now upon a quick look it kinda looks like success:

No need to start compilation, the server, etc, if that directory doesn't exist.

[aranajhonny]

@rauchg with 'next build', the same should send an alert that the ' pages ' don't exist.

[rauchg]

Yep. Great observation @aranajhonny

[aranajhonny]

@rauchg it would be something like this ?