input: Write a function to filter out all negative numbers from the given matrix. The function should return a new matrix where all negative numbers have been replaced with 0s. If the input matrix is empty, the function should return an empty matrix.
  assert filter_out_negative([[-1, 2, -3], [-4, 5, 6], [-7, 8, 9]]).tolist()==[[0, 2, 0], [0, 5, 6], [0, 8, 9]]
  assert filter_out_negative([[1, -2, 3], [4, -5, 6], [7, -8, 9]]).tolist()==[[1, 0, 3], [4, 0, 6], [7, 0, 9]]
  assert filter_out_negative([]).tolist()==[]
  assert filter_out_negative([[0, 0, 0], [0, 0, 0], [0, 0, 0]]).tolist()==[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
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]