[master] Fixed missing log placeholder in b10-dhcp4

Testing undercovered a missing log place holder in Dhcp4_srv.cc, which
surfaces when a release for a non-existance lease is received.
This has been corrected.

src/bin/dhcp4/dhcp4_messages.mes

@@ -295,7 +295,7 @@ intervention (e.g. check if DHCP process has sufficient privileges to
 update the database). It may also be triggered if a lease was manually
 removed from the database during RELEASE message processing.
 
-% DHCP4_RELEASE_FAIL_NO_LEASE client (client-id %2) tried to release address %1, but there is no lease for such address.
+% DHCP4_RELEASE_FAIL_NO_LEASE client (client-id %1, hwaddr %2) tried to release address, %3, but there is no such lease.
 This warning message is printed when client attempts to release a lease,
 but no such lease is known to the server.
 

src/bin/dhcp4/dhcp4_srv.cc

@@ -1276,10 +1276,12 @@ Dhcpv4Srv::processRelease(Pkt4Ptr& release) {
 
         if (!lease) {
             // No such lease - bogus release
-            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL, DHCP4_RELEASE_FAIL_NO_LEASE)
-                .arg(release->getCiaddr().toText())
-                .arg(release->getHWAddr()->toText())
-                .arg(client_id ? client_id->toText() : "(no client-id)");
+            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL,
+                      DHCP4_RELEASE_FAIL_NO_LEASE)
+                      .arg(client_id ? client_id->toText() : "(no client-id)")
+                      .arg(release->getHWAddr() ?
+                           release->getHWAddr()->toText() : "(no hwaddr info)")
+                      .arg(release->getCiaddr().toText());
             return;
         }