resolved: don't check for NULL DnsAnswer object explicitly where unnecessary

The DNS_ANSWER_FOREACH macros do this internally anyway, no need to
duplicate this.

src/resolve/resolved-dns-answer.c

@@ -233,9 +233,6 @@ int dns_answer_find_soa(DnsAnswer *a, const DnsResourceKey *key, DnsResourceReco
 
         assert(key);
 
-        if (!a)
-                return 0;
-
         /* For a SOA record we can never find a matching SOA record */
         if (key->type == DNS_TYPE_SOA)
                 return 0;
@@ -260,9 +257,6 @@ int dns_answer_find_cname_or_dname(DnsAnswer *a, const DnsResourceKey *key, DnsR
 
         assert(key);
 
-        if (!a)
-                return 0;
-
         /* For a {C,D}NAME record we can never find a matching {C,D}NAME record */
         if (key->type == DNS_TYPE_CNAME || key->type == DNS_TYPE_DNAME)
                 return 0;