resolved: keep parsing DNS delegate servers after duplicates

The DNS delegate parser tries to filter duplicate DNS= entries, but the
duplicate branch returned from the whole parser. This made a duplicate
server truncate the rest of the same DNS= line, silently dropping later
valid servers.

Reproducer:

  DNS=192.168.77.78 192.168.77.78 192.168.77.79

Before: only 192.168.77.78 appeared in the delegate server list.

Follow-up for: 7928c0e0a1

(cherry picked from commit 0cfa2d4f4c)

src/resolve/resolved-dns-delegate.c

@@ -281,7 +281,7 @@ int config_parse_delegate_dns_servers(
                         /* Drop the marker. This is used to find the servers that ceased to exist, see
                          * manager_mark_dns_servers() and manager_flush_marked_dns_servers(). */
                         dns_server_move_back_and_unmark(s);
-                        return 0;
+                        continue;
                 }
 
                 r = dns_server_new(

test/units/TEST-75-RESOLVED.sh

@@ -1473,7 +1473,7 @@ testcase_delegate() {
     mkdir -p /run/systemd/dns-delegate.d/
     cat >/run/systemd/dns-delegate.d/testcase.dns-delegate <<EOF
 [Delegate]
-DNS=192.168.77.78
+DNS=192.168.77.78 192.168.77.78 192.168.77.79
 Domains=exercise.test
 FirewallMark=42
 EOF
@@ -1481,6 +1481,7 @@ EOF
     resolvectl status
 
     assert_eq "$(resolvectl --json=short | jq -rc '.[] | select(.delegate == "testcase") | .servers | .[0].addressString')" '192.168.77.78'
+    assert_eq "$(resolvectl --json=short | jq -rc '.[] | select(.delegate == "testcase") | .servers | .[1].addressString')" '192.168.77.79'
     assert_eq "$(resolvectl --json=short | jq -rc '.[] | select(.delegate == "testcase") | .searchDomains | .[0].name')" 'exercise.test'
 
     # Now that we installed the delegation the resolution should fail, because nothing is listening on that IP address