ares_expand_name doesn't guarantee that pointer variable is initialized if
return code is ARES_EBADNAME or ARES_ENOMEM. But current usage of the function
in the codebase thinks otherwise.

There seems to be an assumption that pointer is always initialized even though
it is a local variable and we create a unique pointer soon after calling
ares_expand_name. This could potentially crash
the program with an invalid free pointer.

I was able to crash it by poisoning the memory and some manual hooks.

node(9118,0x111471dc0) malloc: *** error for object 0x7b: pointer being freed was not allocated
node(9118,0x111471dc0) malloc: *** set a breakpoint in malloc_error_break to debug
[1] 9118 abort node ../temp.js

By moving the unique_ptr after checking the return code we can fix the problem.
As the underlying function guarantees that pointer is initialized when the
status is ARES_SUCCESS.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines