refactor(llc, ui): Make Streams non-nullable wherever possible.

Signed-off-by: xsahil03x <[email protected]>

packages/stream_chat_flutter/lib/src/channel_preview.dart

@@ -132,7 +132,7 @@ class ChannelPreview extends StatelessWidget {
                                   message: lastMessage!,
                                   size: channelPreviewTheme.indicatorIconSize,
                                   isMessageRead: channel.state!.read
-                                          ?.where((element) =>
+                                          .where((element) =>
                                               element.user.id !=
                                               channel
                                                   .client.state.currentUser!.id)

packages/stream_chat_flutter/lib/src/message_list_view.dart

@@ -915,7 +915,7 @@ class _MessageListViewState extends State<MessageListView> {
     }
 
     final channel = streamChannel!.channel;
-    final readList = channel.state?.read?.where((read) {
+    final readList = channel.state?.read.where((read) {
           if (read.user.id == userId) return false;
           return read.lastRead.isAfter(message.createdAt) ||
               read.lastRead.isAtSameMomentAs(message.createdAt);
@@ -1204,7 +1204,7 @@ class _MessageListViewState extends State<MessageListView> {
             builder: (_) => BetterStreamBuilder<Message>(
               stream: streamChannel!.channel.state!.messagesStream.map(
                   (messages) =>
-                      messages!.firstWhere((m) => m.id == message.id)),
+                      messages.firstWhere((m) => m.id == message.id)),
               initialData: message,
               builder: (_, data) => StreamChannel(
                 channel: streamChannel!.channel,