input: Write a function to calculate the combined length of two input strings. If both strings are empty then return 0.
  assert get_string_length("Hello", "World")==10
  assert get_string_length("", "World")==5
  assert get_string_length("Hello", "")==5
  assert get_string_length("", "")==0
output: def get_string_length(s1, s2):
      if s1 == "" and s2 == "":
          return 0
      return len(s1) + len(s2)