AC_Avoid: confirm USE_PROXIMITY_SENSOR to check if proximity is enabled

libraries/AC_Avoidance/AC_Avoid.cpp

@@ -390,7 +390,7 @@ void AC_Avoid::adjust_velocity_z(float kP, float accel_cmss, float& climb_rate_c
     // get distance from proximity sensor
     float proximity_alt_diff;
     AP_Proximity *proximity = AP::proximity();
-    if (proximity && _proximity_enabled && proximity->get_upward_distance(proximity_alt_diff)) {
+    if (proximity && proximity_avoidance_enabled() && proximity->get_upward_distance(proximity_alt_diff)) {
         proximity_alt_diff -= _margin;
         if (!limit_alt || proximity_alt_diff < alt_diff) {
             alt_diff = proximity_alt_diff;

libraries/AC_Avoidance/AC_Avoid.h

@@ -81,7 +81,7 @@ public:
 
     // enable/disable proximity based avoidance
     void proximity_avoidance_enable(bool on_off) { _proximity_enabled = on_off; }
-    bool proximity_avoidance_enabled() const { return _proximity_enabled; }
+    bool proximity_avoidance_enabled() const { return (_proximity_enabled && (_enabled & AC_AVOID_USE_PROXIMITY_SENSOR) > 0); }
     void proximity_alt_avoidance_enable(bool on_off) { _proximity_alt_enabled = on_off; }
 
     // helper functions