Only accept 'you left group' messages when group blocked

js/background.js

@@ -920,9 +920,9 @@
       updates.left = true;
     }
 
-    if (details.blocked === true) {
+    if (details.blocked) {
       storage.addBlockedGroup(id);
-    } else if (details.blocked === false) {
+    } else {
       storage.removeBlockedGroup(id);
     }
 

libtextsecure/message_receiver.js

@@ -730,9 +730,12 @@ MessageReceiver.prototype.extend({
         const groupId = message.group && message.group.id;
         const isBlocked = this.isGroupBlocked(groupId);
         const isMe = envelope.source === textsecure.storage.user.getNumber();
-        const hasGroupMetadata = Boolean(message.group);
+        const isLeavingGroup = Boolean(
+          message.group &&
+            message.group.type === textsecure.protobuf.GroupContext.Type.QUIT
+        );
 
-        if (groupId && isBlocked && !(isMe && hasGroupMetadata)) {
+        if (groupId && isBlocked && !(isMe && isLeavingGroup)) {
           window.log.warn(
             `Message ${this.getEnvelopeId(
               envelope
@@ -768,9 +771,12 @@ MessageReceiver.prototype.extend({
         const groupId = message.group && message.group.id;
         const isBlocked = this.isGroupBlocked(groupId);
         const isMe = envelope.source === textsecure.storage.user.getNumber();
-        const hasGroupMetadata = Boolean(message.group);
+        const isLeavingGroup = Boolean(
+          message.group &&
+            message.group.type === textsecure.protobuf.GroupContext.Type.QUIT
+        );
 
-        if (groupId && isBlocked && !(isMe && hasGroupMetadata)) {
+        if (groupId && isBlocked && !(isMe && isLeavingGroup)) {
           window.log.warn(
             `Message ${this.getEnvelopeId(
               envelope