Used the correct type for the AIO preload handler return value.

src/os/unix/ngx_freebsd_sendfile_chain.c

diff --git a/src/os/unix/ngx_freebsd_sendfile_chain.c b/src/os/unix/ngx_freebsd_sendfile_chain.c
index 25790b6..3f17dc6 100644
--- a/src/os/unix/ngx_freebsd_sendfile_chain.c
+++ b/src/os/unix/ngx_freebsd_sendfile_chain.c
@@ -266,9 +266,9 @@
                 c->busy_count = 0;
             }
 
-            rc = aio->preload_handler(file);
+            n = aio->preload_handler(file);
 
-            if (rc > 0) {
+            if (n > 0) {
                 send = prev_send + sent;
                 continue;
             }