Fix: group color change doesn't immediately apply

Because we were fetching a new thread instance, instead of updating the
existing thread instance, classes which were bound to the old thread instance
weren't updating. This affected the HeaderView.AvatarView.thread and the
ConversationStyle.thread.

Signal/src/ViewControllers/ConversationView/ConversationViewController.m

@@ -3239,17 +3239,7 @@ typedef enum : NSUInteger {
 
     if (self.isGroupConversation) {
         [self.uiDatabaseConnection readWithBlock:^(YapDatabaseReadTransaction *transaction) {
-            TSGroupThread *gThread = (TSGroupThread *)self.thread;
-
-            if (gThread.groupModel) {
-                TSGroupThread *_Nullable updatedThread =
-                    [TSGroupThread threadWithGroupId:gThread.groupModel.groupId transaction:transaction];
-                if (updatedThread) {
-                    self.thread = updatedThread;
-                } else {
-                    OWSFailDebug(@"Could not reload thread.");
-                }
-            }
+            [self.thread reloadWithTransaction:transaction];
         }];
         [self updateNavigationTitle];
     }

SignalServiceKit/src/Storage/TSYapDatabaseObject.h

@@ -94,6 +94,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  * Assign the latest persisted values from the database.
  */
+- (void)reloadWithTransaction:(YapDatabaseReadTransaction *)transaction;
 - (void)reload;
 
 /**

SignalServiceKit/src/Storage/TSYapDatabaseObject.m

@@ -220,7 +220,14 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (void)reload
 {
-    TSYapDatabaseObject *latest = [[self class] fetchObjectWithUniqueID:self.uniqueId];
+    [self.dbReadConnection readWithBlock:^(YapDatabaseReadTransaction *_Nonnull transaction) {
+        [self reloadWithTransaction:transaction];
+    }];
+}
+
+- (void)reloadWithTransaction:(YapDatabaseReadTransaction *)transaction
+{
+    TSYapDatabaseObject *latest = [[self class] fetchObjectWithUniqueID:self.uniqueId transaction:transaction];
     if (!latest) {
         OWSFailDebug(@"`latest` was unexpectedly nil");
         return;