Added chat file download indicator

lib/screen/pages/talk/chatBubble.dart

@@ -145,7 +145,13 @@ class _ChatBubbleState extends State<ChatBubble> {
                   left: 0,
                   right: 0,
                   bottom: 0,
-                  child: Center(child: CircularProgressIndicator(value: downloadProgress/100)),
+                  child: Stack(
+                    children: [
+                      const Center(child: Icon(Icons.download)),
+                      const Center(child: CircularProgressIndicator(color: Colors.white)),
+                      Center(child: CircularProgressIndicator(value: downloadProgress/100)),
+                    ],
+                  )
                 ),
               ),
             ],