AP_NavEKF3: Add missing fallback to baro for range beacon use case

libraries/AP_NavEKF3/AP_NavEKF3_PosVelFusion.cpp

@@ -1034,7 +1034,8 @@ void NavEKF3_core::selectHeightForFusion()
     bool lostRngHgt = ((activeHgtSource == HGT_SOURCE_RNG) && ((imuSampleTime_ms - rngValidMeaTime_ms) > 500));
     bool lostGpsHgt = ((activeHgtSource == HGT_SOURCE_GPS) && ((imuSampleTime_ms - lastTimeGpsReceived_ms) > 2000));
     bool lostExtNavHgt = ((activeHgtSource == HGT_SOURCE_EXTNAV) && ((imuSampleTime_ms - extNavMeasTime_ms) > 2000));
-    if (lostRngHgt || lostGpsHgt || lostExtNavHgt) {
+    bool lostRngBcnHgt = ((activeHgtSource == HGT_SOURCE_BCN) && ((imuSampleTime_ms - rngBcnDataDelayed.time_ms) > 2000));
+    if (lostRngHgt || lostGpsHgt || lostExtNavHgt || lostRngBcnHgt) {
         activeHgtSource = HGT_SOURCE_BARO;
     }