fail on blank string

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@6533 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/mod/endpoints/mod_portaudio/mod_portaudio.c

@@ -1556,7 +1556,7 @@ static switch_status_t place_call(char **argv, int argc, switch_stream_handle_t
 	switch_status_t status = SWITCH_STATUS_SUCCESS;
 	char *dest = NULL;
 
-	if (!argv[0]) {
+	if (switch_strlen_zero(argv[0])) {
 		stream->write_function(stream, "FAIL:Usage: call <dest>\n");
 		return SWITCH_STATUS_SUCCESS;
 	}