px4io driver: Only try to upload if we have a non-zero failsafe throttle value

src/drivers/px4io/px4io.cpp

@@ -994,13 +994,17 @@ PX4IO::task_main()
 				int32_t failsafe_param_val;
 				param_t failsafe_param = param_find("RC_FAILS_THR");
 
-				if (failsafe_param > 0) {
+				if (failsafe_param != PARAM_INVALID) {
 
 					param_get(failsafe_param, &failsafe_param_val);
-					uint16_t failsafe_thr = failsafe_param_val;
-					pret = io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_RC_THR_FAILSAFE_US, &failsafe_thr, 1);
-					if (pret != OK) {
-						log("failsafe upload failed");
+
+					if (failsafe_param_val > 0) {
+
+						uint16_t failsafe_thr = failsafe_param_val;
+						pret = io_reg_set(PX4IO_PAGE_SETUP, PX4IO_P_SETUP_RC_THR_FAILSAFE_US, &failsafe_thr, 1);
+						if (pret != OK) {
+							log("failsafe upload failed, FS: %d us", (int)failsafe_thr);
+						}
 					}
 				}