The dns_name_copy() function cannot fail gracefully when the last argument
(target) is NULL. Add RUNTIME_CHECK()s around such calls.
The first semantic patch adds RUNTIME_CHECK() around any call that ignores the
return value and is very safe to apply.
The second semantic patch attempts to properly add RUNTIME_CHECK() to places
where the return value from `dns_name_copy()` is recorded into `result`
variable. The result of this semantic patch needs to be reviewed by hand.
Both patches misses couple places where the code surrounding the
`dns_name_copy(..., NULL)` usage is more complicated and is better suited to be
fixed by a human being that understands the surrounding code.
