Events: fixed eventport handling in ngx_handle_read_event().

The "!rev->ready" test seems to be a typo, introduced in the original
commit (719:f30b1a75fd3b).  The ngx_handle_write_event() code properly
tests for "rev->ready" instead.

Due to this typo, read events might be unexpectedly removed during
proxying after an event on the other part of the proxied connection.
Catched by mail proxying tests.

src/event/ngx_event.c

diff --git a/src/event/ngx_event.c b/src/event/ngx_event.c
index 402a7f5..ed7b30b 100644
--- a/src/event/ngx_event.c
+++ b/src/event/ngx_event.c
@@ -318,7 +318,7 @@
             return NGX_OK;
         }
 
-        if (rev->oneshot && !rev->ready) {
+        if (rev->oneshot && rev->ready) {
             if (ngx_del_event(rev, NGX_READ_EVENT, 0) == NGX_ERROR) {
                 return NGX_ERROR;
             }