Fix race between sync messages and receipts

Previously, when processing a backlog of sync messages and their
delivery receipts, we would fail to mark some messages as delivered even
though we got a receipt. This was due to an async race condition between
saving a sync message and fetching it after the receipt arrives.

Fix by re-ordering idb requests such that we save the message first and
fetch it after.

Fixes #479

// FREEBIE

js/background.js

@@ -238,8 +238,8 @@
             return;
         }
 
-        messages.fetchSentAt(timestamp).then(function() {
-            groups.fetchGroups(pushMessage.source).then(function() {
+        groups.fetchGroups(pushMessage.source).then(function() {
+            messages.fetchSentAt(timestamp).then(function() {
                 var found = false;
                 messages.where({type: 'outgoing'}).forEach(function(message) {
                     var deliveries     = message.get('delivered') || 0;
@@ -264,8 +264,6 @@
                 receipts.add({ timestamp: timestamp, source: pushMessage.source });
                 return;
             });
-        }).fail(function() {
-            console.log('got delivery receipt for unknown message', pushMessage.source, timestamp);
         });
     }
 })();

js/models/messages.js

@@ -352,8 +352,8 @@
                     });
                 }
 
-                conversation.save().then(function() {
-                    message.save().then(function() {
+                message.save().then(function() {
+                    conversation.save().then(function() {
                         conversation.trigger('newmessage', message);
                         conversation.notify(message);
                     });