Fix possibility of requests queueing up in recursive watchHistory call

You can test this manually by delaying the response in
https://github.com/galaxyproject/galaxy/blob/928bb4b4622f57c1fb8d8eecbe4cc9b260e5aab0/lib/galaxy/webapps/galaxy/controllers/history.py#L999
and hitting the refresh button a bunch of times. In the network tab
you'll see the requests piling up.

client/src/store/historyStore/model/watchHistory.js

@@ -22,6 +22,8 @@ let lastUpdateTime = null;
 let lastRequestDate = new Date();
 
 export async function watchHistory() {
+    // "Reset" watchTimeout so we don't queue up watchHistory calls in rewatchHistory.
+    watchTimeout = null;
     // get current history
     const history = await getCurrentHistoryFromServer();
     const historyId = history.id;