Fix code scanning alert no. 1: Potential use after free

[cooljeanius]

Fixes https://github.com/cooljeanius/mdnsd/security/code-scanning/1

To fix the use-after-free issue, we need to ensure that the pointer r->rr.rdata is not accessed after it has been freed unless it is reassigned a valid memory block. Additionally, we should add error handling to check if malloc fails and handle that scenario appropriately.

• First, free the existing memory block pointed to by r->rr.rdata.
• Set the pointer to NULL immediately after freeing it to avoid accidental use.
• Allocate a new memory block and check if the allocation was successful.
• If the allocation fails, handle the error appropriately (e.g., by logging an error message and returning from the function).
• If the allocation succeeds, proceed with copying the data.

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[cooljeanius]

may not fix it, but worth doing anyways