input: Write a function to filter out all negative numbers from the given matrix and replace them with zero. Return the modified matrix. If the input matrix is empty, return an empty matrix.
  assert filter_out_negative([[-1, 2, -3], [-4, 5, 6], [-7, 8, 9]]) == [[0, 2, 0], [0, 5, 6], [0, 8, 9]]
  assert filter_out_negative([[1, -2], [-3, 4]]) == [[1, 0], [0, 4]]
  assert filter_out_negative([[]]) == [[]]
output: def filter_out_negative(matrix):
      if not matrix:
          return []
      return [[0 if x < 0 else x for x in row] for row in matrix]