conf: error out on invalid host id

https://bugzilla.redhat.com/show_bug.cgi?id=1196503

We already check whether the host id is valid or not, add a jump
to forbid invalid host id.

Signed-off-by: Luyao Huang <lhuang@redhat.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>

src/conf/network_conf.c

@@ -717,6 +717,7 @@ virNetworkDHCPHostDefParseXML(const char *networkName,
             virReportError(VIR_ERR_XML_ERROR,
                            _("Invalid character '%c' in id '%s' of network '%s'"),
                            *cp, id, networkName);
+            goto cleanup;
         }
     }