AP_NavEKF2: Handle case where we are in-flight and haven't yet aligned the yaw

This happens if planes are flown without a compass

libraries/AP_NavEKF2/AP_NavEKF2_MagFusion.cpp

@@ -57,6 +57,13 @@ void NavEKF2_core::controlMagYawReset()
         }
     }
 
+    // In-Flight yaw alignment for vehicles that can use a zero sideslip assumption (Planes)
+    // and are not using a compass
+    if (!yawAlignComplete && assume_zero_sideslip() && inFlight) {
+        realignYawGPS();
+        firstMagYawInit = yawAlignComplete;
+    }
+
     // In-Flight reset for vehicles that can use a zero sideslip assumption (Planes)
     // this is done to protect against unrecoverable heading alignment errors due to compass faults
     if (!firstMagYawInit && assume_zero_sideslip() && inFlight) {