Always check for one-item sequences.

With one item in sequence we do not have to roll dice. This holds for
all sorts of dice.

diceware/random_sources.py

@@ -148,12 +148,12 @@ class RealDiceRandomSource(object):
     def choice(self, sequence):
         """Pick one item out of `sequence`.
         """
+        if len(sequence) == 1:
+            return sequence[0]  # no need to roll dice.
         num_rolls = int(math.log(len(sequence), self.dice_sides))
         if num_rolls < 1:
             # If this happens, there are less values in the sequence to
             # choose from than there are dice sides.
-            if len(sequence) == 1:
-                return sequence[0]
             # Check whether len(sequence) is a factor of dice.sides
             if self.dice_sides % len(sequence) == 0:
                 num_rolls = 1