Plane: disable parachute checks when min alt is zero

ArduPlane/parachute.cpp

@@ -40,13 +40,13 @@ bool Plane::parachute_manual_release()
     }
 
     // do not release if vehicle is not flying
-    if (!is_flying()) {
+    if (!is_flying() && parachute.alt_min() != 0) {
         // warn user of reason for failure
         gcs_send_text(MAV_SEVERITY_WARNING,"Parachute: Not flying");
         return false;
     }
 
-    if (relative_ground_altitude() < parachute.alt_min()) {
+    if (parachute.alt_min() != 0 && relative_ground_altitude() < parachute.alt_min()) {
         gcs_send_text_fmt(MAV_SEVERITY_WARNING, "Parachute: Too low");
         return false;
     }