input: Write a python function to fill missing values in an array with the last found non-missing value.
  assert fillMissingValues([3, 7, -1, 4, 5, 6, -1, 1], 8) == [3, 7, 7, 4, 5, 6, 6, 1]
  assert fillMissingValues([-1, -1, 5, 6, -1], 5) == [5, 5, 5, 6, 6]
  assert fillMissingValues([1, 2, -1, -1, 3, 4, -1], 7) == [1, 2, 2, 2, 3, 4, 4]
output: def fillMissingValues(arr, n):
      last_value = None
      for i in range(n):
          if arr[i] != -1:
              last_value = arr[i]
          elif last_value is not None:
              arr[i] = last_value
      return arr