Don't print %!s(nil) when ierr is nil. (#2803)
Don't print %!s(nil) when ierr is nil. (#2803)

Sometimes sendError gets a nil argument for ierr (internal error). When this
happens we print a line like:

[AUDIT] Internal error - Failed to get registration by key - %!s(<nil>)

This is fine but distracting, since it looks like a logging bug.
Instead, print a shorter message with just the external-facing problem.
ibukanov/boulder,jcjones/boulder,lucasallan/boulder,jcjones/boulder,lucasallan/boulder,jsha/boulder,letsencrypt/boulder,jfrazelle/boulder,bmw/boulder,ibukanov/boulder,jfrazelle/boulder,jfrazelle/boulder,jsha/boulder,jcjones/boulder,lucasallan/boulder,ibukanov/boulder,jfrazelle/boulder,letsencrypt/boulder,bmw/boulder,jsha/boulder,letsencrypt/boulder,jcjones/boulder,bmw/boulder