Revert "Remove haiku_host/Errors.h"

This reverts commit f105756e273ccff786618c049ea97ac7c9c7b501.

The host header gets included if this file is missing , rather than the
one in the build tree. Fix the build again.
Fix off-by-one error

This would cause the last char before the hostname to sometimes stay
bold and not be properly reset to a regular font.

Fixes #10982.