Avoid querying groups on delivery receipts if possible

js/delivery_receipts.js

@@ -41,17 +41,23 @@
         },
         onReceipt: function(receipt) {
             var messages  = new Whisper.MessageCollection();
+            messages.fetchSentAt(receipt.get('timestamp')).then(function() {
+                if (messages.length === 0) { return; }
+                var message = messages.find(function(message) {
+                    return (!message.isIncoming() && receipt.get('source') === message.get('conversationId'));
+                });
+                if (message) { return message; }
+
                 var groups    = new GroupCollection();
-            Promise.all([
-                groups.fetchGroups(receipt.get('source')),
-                messages.fetchSentAt(receipt.get('timestamp'))
-            ]).then(function() {
+                return groups.fetchGroups(receipt.get('source')).then(function() {
                     var ids = groups.pluck('id');
                     ids.push(receipt.get('source'));
-                var message = messages.find(function(message) {
+                    return messages.find(function(message) {
                         return (!message.isIncoming() &&
                                 _.contains(ids, message.get('conversationId')));
                     });
+                });
+            }).then(function(message) {
                 if (message) {
                     this.remove(receipt);
                     var deliveries = message.get('delivered') || 0;