input: Write a function to filter out all negative numbers from the given matrix. The function should return the matrix with all negative numbers replaced by zeros. If the given matrix is empty, the function should 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([[]])==[[]]
  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]