input: Write a function to take in two strings as input, and output a list of all the words in both strings. If the two strings are given, split each string into words and concatenate the two resulting lists. Return the concatenated list. If either input string is empty or both are empty, return an empty list.
  assert string_to_list("I want to make a difference", "The journey to success is long") == ['I', 'want', 'to', 'make', 'a', 'difference', 'The', 'journey', 'to', 'success', 'is', 'long']
  assert string_to_list("", "The journey to success is long") == ['The', 'journey', 'to', 'success', 'is', 'long']
  assert string_to_list("I want to make a difference", "") == ['I', 'want', 'to', 'make', 'a', 'difference']
  assert string_to_list("", "") == []
  assert string_to_list("Only one word", "Another single") == ['Only', 'one', 'word', 'Another', 'single']
output: def string_to_list(str1, str2):
      if not str1 and not str2:
          return []
      if not str1:
          return str2.split()
      if not str2:
          return str1.split()
      return str1.split() + str2.split()