Fix EOF for buffered app protocol

[fantix]

UV_EOF is given to read_cb() on EOF, which causes an error like this:

Unexpected calls to loop.call_exception_handler():
[{'exception': RuntimeError('no python buffer is allocated in on_read; nread=-4095',),
  'message': 'Fatal error on transport UnixTransport',
  'protocol': <uvloop.loop.SSLProtocol object at 0x7f1749684630>,
  'transport': <UnixTransport closed=True reading=False 0x7f17496eb6c8>},
 {'exception': RuntimeError('no python buffer is allocated in on_read; nread=-4095',),
  'message': 'Fatal error on transport UnixTransport',
  'protocol': <uvloop.loop.SSLProtocol object at 0x7f1749650470>,
  'transport': <UnixTransport closed=True reading=False 0x7f1749643a08>}]
FAIL

======================================================================
FAIL: test_create_unix_connection_ssl_1 (tests.test_unix.Test_UV_UnixSSL)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/decentfox/uvloop/uvloop/_testbase.py", line 102, in tearDown
    self.fail('unexpected calls to loop.call_exception_handler()')
AssertionError: unexpected calls to loop.call_exception_handler()

This failing test was found in #176, but it was unstable. Let me try to make a stable test for this fix.

Related upstream issue: joyent/libuv#803

[fantix]

Added test - took some time to figure out how to reproduce the "EPOLLHUP with data" scenario. Now the test is stably failing without the fix.

[1st1]

Awesome, thanks!