uasyncio.core: Optimize case of resuming coro with no args.

Don't create a new tuple with empty arguments for coro.send(), just use
next(coro).

uasyncio.core/uasyncio/core.py

@@ -64,10 +64,11 @@ class EventLoop:
             else:
                 delay = 0
                 try:
-                    if args == ():
-                        args = (None,)
                     if __debug__:
                         log.debug("Coroutine %s send args: %s", cb, args)
+                    if args == ():
+                        ret = next(cb)
+                    else:
                         ret = cb.send(*args)
                     if __debug__:
                         log.debug("Coroutine %s yield result: %s", cb, ret)