Restored zeroing of ngx_channel_t in ngx_pass_open_channel().

Due to structure's alignment, some uninitialized memory contents may have
been passed between processes.

Zeroing was removed in 0215ec9aaa8a.

Reported by Johnny Wang.

src/os/unix/ngx_process_cycle.c

diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
index b31485f..07cd05e 100644
--- a/src/os/unix/ngx_process_cycle.c
+++ b/src/os/unix/ngx_process_cycle.c
@@ -398,6 +398,8 @@
     ngx_int_t      i;
     ngx_channel_t  ch;
 
+    ngx_memzero(&ch, sizeof(ngx_channel_t));
+
     ch.command = NGX_CMD_OPEN_CHANNEL;
     ch.pid = ngx_processes[ngx_process_slot].pid;
     ch.slot = ngx_process_slot;