preload just a single byte to avoid testing file overrun

src/http/ngx_http_copy_filter_module.c

diff --git a/src/http/ngx_http_copy_filter_module.c b/src/http/ngx_http_copy_filter_module.c
index 954717d..8f4002f 100644
--- a/src/http/ngx_http_copy_filter_module.c
+++ b/src/http/ngx_http_copy_filter_module.c
@@ -171,7 +171,7 @@
             c->busy_sendfile = NULL;
             e = (ngx_http_ephemeral_t *) &r->uri_start;
 
-            n = ngx_file_aio_read(file, e->preload, 4, offset, r->pool);
+            n = ngx_file_aio_read(file, e->aio_preload, 1, offset, r->pool);
 
             if (n > 0) {
                 continue;

src/http/ngx_http_request.h

diff --git a/src/http/ngx_http_request.h b/src/http/ngx_http_request.h
index 2ca2153..3bd70c3 100644
--- a/src/http/ngx_http_request.h
+++ b/src/http/ngx_http_request.h
@@ -547,7 +547,7 @@
 typedef struct {
     ngx_http_posted_request_t         terminal_posted_request;
 #if (NGX_HAVE_AIO_SENDFILE)
-    u_char                            preload[4];
+    u_char                            aio_preload;
 #endif
 } ngx_http_ephemeral_t;