fix building on 64-bit platforms, introduced in r3025

src/core/ngx_file.c

diff --git a/src/core/ngx_file.c b/src/core/ngx_file.c
index 3db728f..dff5226 100644
--- a/src/core/ngx_file.c
+++ b/src/core/ngx_file.c
@@ -693,7 +693,7 @@
 
     len = cf->buf_size ? cf->buf_size : 65536;
 
-    if (len > size) {
+    if ((off_t) len > size) {
         len = (size_t) size;
     }
 
@@ -713,7 +713,7 @@
 
     while (size > 0) {
 
-        if (len > size) {
+        if ((off_t) len > size) {
             len = (size_t) size;
         }