fix: clear price after send

lib/ui/sell_page/widgets/sell_page.dart

@@ -172,6 +172,7 @@ class _SellPageState extends State<SellPage> {
                                     behavior: SnackBarBehavior.floating,
                                   ),
                                 );
+                                price.clear();
                                 return;
                               },
                               icon: Icon(Icons.check),