ipa_proxy: make sure ipa instance name is nul-terminated

Reported by coverity. CID 1206565.
diff --git a/src/ipa_proxy.c b/src/ipa_proxy.c
index 0c177a2..6053bb8 100644
--- a/src/ipa_proxy.c
+++ b/src/ipa_proxy.c
@@ -246,6 +246,7 @@
 		return CMD_WARNING;
 	}
 	strncpy(ipi->name, argv[0], IPA_INSTANCE_NAME);
+	ipi->name[IPA_INSTANCE_NAME - 1] = '\0';
 	ipi->net.type = type;
 	ipi->net.addr = talloc_strdup(tall_ipa_proxy_ctx, argv[2]);
 	ipi->net.port = port;