Wake JS on libuv poll errors instead of dropping the callback

[nigrosimone]

on_io_readable and on_io_writable look only at revents. But libuv signals a poll error with
status < 0 and revents == 0, and before calling the callback it already runs uv__io_stop and
uv__handle_stop, so the fd is out of the loop and no other event can arrive.

The result is that a connection reset by the peer becomes silent while it still looks alive.

I found it with pipelined queries in pg-native, where losing a backend in the middle of a batch left
the client with a connection that never completes and never fails.

[brianc]

amazing job on writing tests for this, ty!!

[nigrosimone]

The tests are success, but the ci hang to exit

[nigrosimone]

@brianc my bad! my test don't close the sockets connections in https://github.com/brianc/node-libpq/pull/137/changes#diff-399651cdf8269b054efafa4155e009dbcb08f02e1fa57847e25d387974a8911eR34 I need to push a fix for the test

afterEach(function (done) {
  sockets.forEach(function (s) { s.destroy() }) // close all sockets
  proxy.close(function () { done() }) 
})

done 5c96d5b