recipetool: Handle unclean response in go resolver

It appears that some go modules repond with a 404 error when trying to
resolve them dynamically. The response body may still contain the
go-import meta tag. An example for such behaviour is gonum.org/v1/gonum.

Signed-off-by: Sven Schwermer <sven.schwermer@disruptive-technologies.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>