fix: no new msg notifications after opening chat modal [NATIVE]

call TOGGLE_CHAT action when chat modal is closed to correctly update chat isOpen state

react/features/chat/components/native/Chat.js

                 headerProps = {{
                     headerLabelKey: 'chat.title'
                 }}
-                modalId = { CHAT_VIEW_MODAL_ID }>
+                modalId = { CHAT_VIEW_MODAL_ID }
+                onClose = { this.props._onToggleChat }>
+
                 <MessageContainer messages = { this.props._messages } />
                 <MessageRecipient />
                 <ChatInputBar onSend = { this.props._onSendMessage } />