MT5 error 4806: Requested data not found

int ma_handle = INVALID_HANDLE;

int OnInit()
  {
   ma_handle = iMA(_Symbol, PERIOD_CURRENT, 50, 0, MODE_SMA, PRICE_CLOSE);
   return(INIT_SUCCEEDED);
  }

void OnTick()
  {
   double ma[];
   CopyBuffer(ma_handle, 0, 0, 3, ma);       // -1 and error 4806 while the MA is still calculating
   Print("MA now: ", ma[2]);                  // and then an array out of range
  }

int ma_handle = INVALID_HANDLE;

int OnInit()
  {
   ma_handle = iMA(_Symbol, PERIOD_CURRENT, 50, 0, MODE_SMA, PRICE_CLOSE);
   return(ma_handle == INVALID_HANDLE ? INIT_FAILED : INIT_SUCCEEDED);
  }

void OnTick()
  {
   double ma[];
   if(BarsCalculated(ma_handle) < 3)          // still calculating: try again on the next tick
      return;
   if(CopyBuffer(ma_handle, 0, 0, 3, ma) != 3)
     {
      Print("CopyBuffer failed: ", GetLastError());
      return;
     }
   Print("MA now: ", ma[2]);
  }