Unified handling of ngx_create_temp_file() return value.

The original check for NGX_AGAIN was surplus, since the function returns
only NGX_OK or NGX_ERROR.  Now it looks similar to other places.

No functional changes.

src/core/ngx_file.c

diff --git a/src/core/ngx_file.c b/src/core/ngx_file.c
index 7e6e921..1cafb82 100644
--- a/src/core/ngx_file.c
+++ b/src/core/ngx_file.c
@@ -114,7 +114,7 @@
         rc = ngx_create_temp_file(&tf->file, tf->path, tf->pool,
                                   tf->persistent, tf->clean, tf->access);
 
-        if (rc == NGX_ERROR || rc == NGX_AGAIN) {
+        if (rc != NGX_OK) {
             return rc;
         }