Request body: removed surplus assigment, no functional changes.

Setting rb->bufs to NULL is surplus after ngx_http_write_request_body()
has returned NGX_OK.
diff --git a/src/http/ngx_http_request_body.c b/src/http/ngx_http_request_body.c
index 77e92e3..e9562c0 100644
--- a/src/http/ngx_http_request_body.c
+++ b/src/http/ngx_http_request_body.c
@@ -172,9 +172,6 @@
                 b->file = &rb->temp_file->file;
 
                 rb->bufs = cl;
-
-            } else {
-                rb->bufs = NULL;
             }
         }
 
@@ -466,9 +463,6 @@
             b->file = &rb->temp_file->file;
 
             rb->bufs = cl;
-
-        } else {
-            rb->bufs = NULL;
         }
     }