Fix markRead when messages have not been loaded yet

Query the database and not just the in-memory messages.

// FREEBIE

js/models/conversations.js

@@ -210,18 +210,18 @@
                 conversationId: conversationId
             }));
 
-            var readReceipts = this.messageCollection.where({
+            this.getUnread().then(function(unreadMessages) {
-                type: 'incoming', unread: 1
+                var read = unreadMessages.map(function(m) {
-            }).map(function(m) {
                     m.markRead();
                     return {
                         sender    : m.get('source'),
                         timestamp : m.get('sent_at')
                     };
-            }.bind(this));
+                });
-            if (readReceipts.length > 0) {
+                if (read.length > 0) {
-                textsecure.messaging.sendReadReceipts(readReceipts);
+                    textsecure.messaging.sendReadReceipts(read);
                 }
+            });
         }
     },