input: Write a function to generate a two-dimensional array filled with zeros based on given row and column numbers. If the input is invalid (negative or non-integer), return None.
  assert generate_zeros_array(3, 3)==[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
  assert generate_zeros_array(2, 4)==[[0, 0, 0, 0], [0, 0, 0, 0]]
  assert generate_zeros_array(-1, 3)==None
  assert generate_zeros_array(0, 0)==[]
  assert generate_zeros_array(5, 0)==[[], [], [], [], []]
output: def generate_zeros_array(rows, cols):
      if not isinstance(rows, int) or not isinstance(cols, int) or rows < 0 or cols < 0:
          return None
      return [[0] * cols for _ in range(rows)]