client: prohibit endpoint ids without @ character

The function mgcp_msg_gen() does only check if the user supplied
an endpoint name or not. The user may still supply an endpoint
name that does not contain the separator (@) character.

- Refuse to generate the message if the endpoint name does not
  contain any @ character.

Change-Id: I92dd1556e4a26b4bef8e1c8c57141552abf988ca
diff --git a/src/libosmo-mgcp-client/mgcp_client.c b/src/libosmo-mgcp-client/mgcp_client.c
index 593d305..efe1d1f 100644
--- a/src/libosmo-mgcp-client/mgcp_client.c
+++ b/src/libosmo-mgcp-client/mgcp_client.c
@@ -862,6 +862,14 @@
 			msgb_free(msg);
 			return NULL;
 		}
+
+		if (strstr(mgcp_msg->endpoint, "@") == NULL) {
+			LOGP(DLMGCP, LOGL_ERROR,
+			     "Endpoint name (%s) lacks separator (@), can not generate MGCP message\n",
+			     mgcp_msg->endpoint);
+			msgb_free(msg);
+		}
+
 		rc += msgb_printf(msg, " %s", mgcp_msg->endpoint);
 	}