minor fixes [skip ci]

lib/src/screens/nano/nano_change_rep_page.dart

@@ -194,7 +194,6 @@ class NanoChangeRepPage extends BasePage {
                   buttonText: S.of(context).ok,
                   buttonAction: () => Navigator.pop(context));
             });
-        throw e;
       }
     }
   }

lib/src/screens/send/widgets/send_card.dart

@@ -195,6 +195,10 @@ class SendCardState extends State<SendCard> with AutomaticKeepAliveClientMixin<S
     PaymentRequest paymentRequest,
     PaymentFlowResult result,
   ) async {
+    if (!context.mounted) {
+      return;
+    }
+
     await showModalBottomSheet<void>(
       context: context,
       isDismissible: true,
@@ -228,6 +232,10 @@ class SendCardState extends State<SendCard> with AutomaticKeepAliveClientMixin<S
     WalletSwitcherViewModel walletSwitcherViewModel,
     PaymentRequest paymentRequest,
   ) async {
+    if (!context.mounted) {
+      return;
+    }
+
     await showModalBottomSheet<void>(
       context: context,
       isDismissible: true,