Close files opened in static file handler (#2118)

* Close files opened in static file handler

* Do not use defer

routergroup.go

@@ -193,13 +193,15 @@ func (group *RouterGroup) createStaticHandler(relativePath string, fs http.FileS
 
 		file := c.Param("filepath")
 		// Check if file exists and/or if we have permission to access it
-		if _, err := fs.Open(file); err != nil {
+		f, err := fs.Open(file)
+		if err != nil {
 			c.Writer.WriteHeader(http.StatusNotFound)
 			c.handlers = group.engine.noRoute
 			// Reset index
 			c.index = -1
 			return
 		}
+		f.Close()
 
 		fileServer.ServeHTTP(c.Writer, c.Request)
 	}