fixed memory leak when session.send coroutine is cancelled (#311)

added that when session.send coroutine is cancelled (or if any other exception is raised) the result should still be removed from the results list

pyrogram/session/session.py

@@ -382,8 +382,8 @@ class Session:
                 await asyncio.wait_for(self.results[msg_id].event.wait(), timeout)
             except asyncio.TimeoutError:
                 pass
-
-            result = self.results.pop(msg_id).value
+            finally:
+                result = self.results.pop(msg_id).value
 
             if result is None:
                 raise TimeoutError