snmp_output_err_resp, snmp_output_resp: allocate `object` using calloc, not

snmp_output_err_resp, snmp_output_resp: allocate `object` using calloc, not
on the stack

Some of the callers try to determine whether or not `object` is valid by
testing the value for NULL, which will never be true if it's a stack value,
so in order to be clear and correct down the call stack, use a heap
allocated object.

This also addresses a Coverity issue by initializing all of `object` via
calloc

MFC after:	1 week
Reported by:	Coverity
CID:		1006392