Zero allocated elements before initializing them
Zero allocated elements before initializing them

For some error conditions, the error handler depends on
ctx->thr[idx]->dnsbase to be zeroed expicitly after allocation.
To prevent this type of error, zero all allocated memory even
though it will get written to in any case.

mimimitm/sslsplit,heavilessrose/sslsplit,heavilessrose/sslsplit,mimimitm/sslsplit,DJMIN/sslsplit,DJMIN/sslsplit