Merge pull request #499 from mattermost/MM-2033

MM-2033 fixes img showing infinity progress

api/file.go

@@ -347,6 +347,7 @@ func getFile(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Cache-Control", "max-age=2592000, public")
+	w.Header().Set("Content-Length", strconv.Itoa(len(f)))
 	w.Write(f)
 }