input: Write a function to filter out all negative numbers from a given matrix and set them to 0. Return the modified matrix. If the 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([]) == []
  assert filter_out_negative([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
  assert filter_out_negative([[-1, -2], [-3, -4]]) == [[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]