Return an error if the device or firmware image is missing from the command line.
diff --git a/rmi4update/main.cpp b/rmi4update/main.cpp
index a873e63..2a0eaf5 100644
--- a/rmi4update/main.cpp
+++ b/rmi4update/main.cpp
@@ -47,9 +47,13 @@
 
 	if (optind < argc)
 		deviceName = argv[optind++];
+	else
+		return -1;
 
 	if (optind < argc)
 		firmwareName = argv[optind];
+	else
+		return -1;
 
 	rc = rmidevice.Open(deviceName);
 	if (rc) {