fix chat fetcher stops, change fetcher code

src/modules/chats.js

@@ -112,14 +112,14 @@ const chats = {
     setChatListFetcher (state, { commit, fetcher }) {
       const prevFetcher = state.chatListFetcher
       if (prevFetcher) {
-        prevFetcher()
+        prevFetcher.stop()
       }
       state.chatListFetcher = fetcher && fetcher()
     },
     setCurrentChatFetcher (state, { fetcher }) {
       const prevFetcher = state.fetcher
       if (prevFetcher) {
-        prevFetcher()
+        prevFetcher.stop()
       }
       state.fetcher = fetcher && fetcher()
     },

src/services/promise_interval/promise_interval.js

@@ -8,9 +8,8 @@
 export const promiseInterval = (promiseCall, interval) => {
   let stopped = false
   let timeout = null
-  let func = () => {}
 
-  func = () => {
+  const func = () => {
     promiseCall().finally(() => {
       if (stopped) return
       timeout = window.setTimeout(func, interval)