AP_TECS: Ensure no throttle output if is_gliding flag is true when flying without airspeed.

libraries/AP_TECS/AP_TECS.cpp

@@ -770,6 +770,7 @@ void AP_TECS::_update_throttle_without_airspeed(int16_t throttle_nudge)
     if (_flags.is_gliding)
     {
         _throttle_dem = 0.0f;
+        return;
     }
 
     // Calculate additional throttle for turn drag compensation including throttle nudging