Properly track progress of smaller file uploads

ngx_http_uploadprogress_module.c

     up->length = 0;
     up->timeout = 0;
 
+    // Properly handles small files where no read events happen after the
+    // request is first handled
+    if (r->headers_in.content_length_n) {
+        up->length = r->headers_in.content_length_n;
+        if (r->request_body) {
+            up->rest = r->request_body->rest;
+        }
+    }
+
     up->next = ctx->list_head.next;
     up->next->prev = up;
     up->prev = &ctx->list_head;