Never store invalid OO checkpoints

www/common/onlyoffice/inner.js

@@ -477,6 +477,18 @@ define([
         var saveToServer = function () {
             if (APP.cantCheckpoint) { return; } // TOO_LARGE
             var text = getContent();
+            text = undefined;
+            if (!text) {
+                setEditable(false, true);
+                sframeChan.query('Q_CLEAR_CACHE_CHANNELS', [
+                    'chainpad',
+                    content.channel,
+                ], function () {});
+                UI.alert(Messages.realtime_unrecoverableError, function () {
+                    common.gotoURL();
+                });
+                return;
+            }
             var blob = new Blob([text], {type: 'plain/text'});
             var file = getFileType();
             blob.name = (metadataMgr.getMetadataLazy().title || file.doc) + '.' + file.type;

www/common/sframe-common-outer.js

@@ -1533,6 +1533,16 @@ define([
             sframeChan.on('Q_CLEAR_CACHE', function (data, cb) {
                 Utils.Cache.clear(cb);
             });
+            sframeChan.on('Q_CLEAR_CACHE_CHANNELS', function (channels, cb) {
+                if (!Array.isArray(channels)) { return void cb({error: "NOT_AN_ARRAY"}); }
+                nThen(function (waitFor) {
+                    channels.forEach(function (chan) {
+                        if (chan === "chainpad") { chan = secret.channel; }
+                        console.error(chan);
+                        Utils.Cache.clearChannel(chan, waitFor());
+                    });
+                }).nThen(cb);
+            });
 
             sframeChan.on('Q_PIN_GET_USAGE', function (teamId, cb) {
                 Cryptpad.isOverPinLimit(teamId, function (err, overLimit, data) {