made Logs dump with dump 0 or -1

ArduCopter/Log.pde

@@ -108,7 +108,7 @@ dump_log(uint8_t argc, const Menu::arg *argv)
 	// check that the requested log number can be read
 	dump_log = argv[1].i;
 	last_log_num = g.log_last_filenumber;
-	if (dump_log == -1) {
+	if (dump_log <= 0) {
 		Serial.printf_P(PSTR("dumping all\n"));
 		Log_Read(1, DF_LAST_PAGE);
 		return(-1);