Ignore missing members in incoming group updates

Previously, updateNumbers would throw an Error, so the whole group
update was discarded.

Signal-Android handles this the same way in
GroupMessageProcessor.handleGroupUpdate().

Closes #1056

js/libtextsecure.js

@@ -36987,19 +36987,9 @@ Internal.SessionLock.queueJobForNumber = function queueJobForNumber(number, runJ
                 if (numbers.filter(textsecure.utils.isNumberSane).length < numbers.length)
                     throw new Error("Invalid number in new group members");
 
-                if (group.numbers.filter(function(number) { return numbers.indexOf(number) < 0 }).length > 0)
-                    throw new Error("Attempted to remove numbers from group with an UPDATE");
-
                 var added = numbers.filter(function(number) { return group.numbers.indexOf(number) < 0; });
 
-                return textsecure.storage.groups.addNumbers(groupId, added).then(function(newGroup) {
+                return textsecure.storage.groups.addNumbers(groupId, added);
-                    if (numbers.filter(function(number) { return newGroup.indexOf(number) < 0; }).length != 0 ||
-                        newGroup.filter(function(number) { return numbers.indexOf(number) < 0; }).length != 0) {
-                        throw new Error("Error calculating group member difference");
-                    }
-
-                    return added;
-                });
             });
         },
 

js/models/messages.js

@@ -345,10 +345,10 @@
                                     groupId    : dataMessage.group.id,
                                     name       : dataMessage.group.name,
                                     avatar     : dataMessage.group.avatar,
-                                    members    : dataMessage.group.members,
+                                    members    : _.union(dataMessage.group.members, conversation.get('members')),
                                 };
                                 group_update = conversation.changedAttributes(_.pick(dataMessage.group, 'name', 'avatar')) || {};
-                                var difference = _.difference(dataMessage.group.members, conversation.get('members'));
+                                var difference = _.difference(attributes.members, conversation.get('members'));
                                 if (difference.length > 0) {
                                     group_update.joined = difference;
                                 }

libtextsecure/storage/groups.js

@@ -139,19 +139,9 @@
                 if (numbers.filter(textsecure.utils.isNumberSane).length < numbers.length)
                     throw new Error("Invalid number in new group members");
 
-                if (group.numbers.filter(function(number) { return numbers.indexOf(number) < 0 }).length > 0)
-                    throw new Error("Attempted to remove numbers from group with an UPDATE");
-
                 var added = numbers.filter(function(number) { return group.numbers.indexOf(number) < 0; });
 
-                return textsecure.storage.groups.addNumbers(groupId, added).then(function(newGroup) {
+                return textsecure.storage.groups.addNumbers(groupId, added);
-                    if (numbers.filter(function(number) { return newGroup.indexOf(number) < 0; }).length != 0 ||
-                        newGroup.filter(function(number) { return numbers.indexOf(number) < 0; }).length != 0) {
-                        throw new Error("Error calculating group member difference");
-                    }
-
-                    return added;
-                });
             });
         },