cleancleanup, prevent null deref.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@6720 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/mod/endpoints/mod_portaudio/mod_portaudio.c

@@ -1730,6 +1730,11 @@ SWITCH_STANDARD_API(pa_cmd)
 		goto done;
 	}
 
+	if (!argv[0]) {
+		stream->write_function(stream, "Unknown Command\n");
+		goto done;
+	}
+
 	if (!strcasecmp(argv[0], "call")) {
 		func = place_call;
 	} else if (!strcasecmp(argv[0], "help")) {