Fix broken stacktrace navigation to references of the form `foo/eval16959/fn`

I closed #850 prematurely and cannot reopen it now. The problem is not fixed. Sometimes info middleware doesn't return file location. In those cases just pick the file from stacktrace.
The example that I have in mind is indeed has to do to the error in the middleware but with the old code user will not notice that because the message "No source location found" overshados the middleware error.

With the new code, you are taken to the location but the error in the middleware is also displayed.