input: Write a function to combine two strings and reverse the result in Python. The function should return the reversed result after combining the given two strings. If either of the strings is empty, the function should return the reversed result of the non-empty string.
  assert reverse_combined_strings("Hello ", "world!")=="!dlrow olleH"
  assert reverse_combined_strings("A ", "B")=="B A"
  assert reverse_combined_strings("Python", "")=="nohtyP"
  assert reverse_combined_strings("", "Java")=="avaJ"
  assert reverse_combined_strings("", "")==""
output: def reverse_combined_strings(s1, s2):
      combined = s1 + s2
      return combined[::-1]