Fix group update avatar handling

The avatar handler was being added to the list of promises too late,
so we were storing the raw avatar protobuf (Long id, bytes key) rather
than the downloaded/decrypted attachment data.

Fixes #280

js/libtextsecure.js

@@ -38781,14 +38781,18 @@ function processDecrypted(decrypted, source) {
 
     if (decrypted.group !== null) {
         decrypted.group.id = getString(decrypted.group.id);
+
+        if (decrypted.group.type == textsecure.protobuf.GroupContext.Type.UPDATE) {
+            if (decrypted.group.avatar !== null) {
+                promises.push(handleAttachment(decrypted.group.avatar));
+            }
+        }
+
         promises.push(textsecure.storage.groups.getNumbers(decrypted.group.id).then(function(existingGroup) {
             if (existingGroup === undefined) {
                 if (decrypted.group.type != textsecure.protobuf.GroupContext.Type.UPDATE) {
                     throw new Error("Got message for unknown group");
                 }
-                if (decrypted.group.avatar !== null) {
-                    promises.push(handleAttachment(decrypted.group.avatar));
-                }
                 return textsecure.storage.groups.createNewGroup(decrypted.group.members, decrypted.group.id);
             } else {
                 var fromIndex = existingGroup.indexOf(source);
@@ -38800,9 +38804,6 @@ function processDecrypted(decrypted, source) {
 
                 switch(decrypted.group.type) {
                 case textsecure.protobuf.GroupContext.Type.UPDATE:
-                    if (decrypted.group.avatar !== null)
-                        promises.push(handleAttachment(decrypted.group.avatar));
-
                     return textsecure.storage.groups.updateNumbers(
                         decrypted.group.id, decrypted.group.members
                     ).then(function(added) {

libtextsecure/helpers.js

@@ -170,14 +170,18 @@ function processDecrypted(decrypted, source) {
 
     if (decrypted.group !== null) {
         decrypted.group.id = getString(decrypted.group.id);
+
+        if (decrypted.group.type == textsecure.protobuf.GroupContext.Type.UPDATE) {
+            if (decrypted.group.avatar !== null) {
+                promises.push(handleAttachment(decrypted.group.avatar));
+            }
+        }
+
         promises.push(textsecure.storage.groups.getNumbers(decrypted.group.id).then(function(existingGroup) {
             if (existingGroup === undefined) {
                 if (decrypted.group.type != textsecure.protobuf.GroupContext.Type.UPDATE) {
                     throw new Error("Got message for unknown group");
                 }
-                if (decrypted.group.avatar !== null) {
-                    promises.push(handleAttachment(decrypted.group.avatar));
-                }
                 return textsecure.storage.groups.createNewGroup(decrypted.group.members, decrypted.group.id);
             } else {
                 var fromIndex = existingGroup.indexOf(source);
@@ -189,9 +193,6 @@ function processDecrypted(decrypted, source) {
 
                 switch(decrypted.group.type) {
                 case textsecure.protobuf.GroupContext.Type.UPDATE:
-                    if (decrypted.group.avatar !== null)
-                        promises.push(handleAttachment(decrypted.group.avatar));
-
                     return textsecure.storage.groups.updateNumbers(
                         decrypted.group.id, decrypted.group.members
                     ).then(function(added) {