[commands] Split Cooldown state processing to two different functions.

This allows us to check if we are rate limited without
creating a new cool-down window for the command.

discord/ext/commands/cooldowns.py

@@ -48,20 +48,27 @@ class Cooldown:
         if not isinstance(self.type, BucketType):
             raise TypeError('Cooldown type must be a BucketType')
 
-    def is_rate_limited(self):
+    def get_tokens(self, current=None):
+        if not current:
+            current = time.time()
+
+        tokens = self._tokens
+
+        if current > self._window + self.per:
+            tokens = self.rate
+        return tokens
+
+    def update_rate_limit(self):
         current = time.time()
         self._last = current
 
+        self._tokens = self.get_tokens(current)
+
         # first token used means that we start a new rate limit window
         if self._tokens == self.rate:
             self._window = current
 
-        # check if our window has passed and we can refresh our tokens
-        if current > self._window + self.per:
-            self._tokens = self.rate
-            self._window = current
-
-        # check if we're rate limited
+        # check if we are rate limited
         if self._tokens == 0:
             return self.per - (current - self._window)