Completion of error handling

[elfring]

Would you like to add more error handling for return values from functions like the following?

• fwrite ⇒ create_pidfile
• malloc ⇒ dns_unpack

[ithewei]

Thanks for your attention and suggestions, it has been processed.

[elfring]

Thanks for your small source code improvement.

I suggest to avoid ignorance of return values a bit more.
Would you like to detect every error situation as early as possible?