input: Write a function to combine 2 given strings and return the reversed result in Python. If any of the strings is an empty string, return an empty string.
  
  assert combine_reverse("Hello ", "world!")=="!dlrow olleH"
  assert combine_reverse("Hi", " there")=="ereht iH"
  assert combine_reverse("Test", "")==""
  assert combine_reverse("", "String")==""
  assert combine_reverse("", "")==""
output: def combine_reverse(str1, str2):
      if str1 == "" or str2 == "":
          return ""
      combined = str1 + str2
      return combined[::-1]