Catch and redirect exception in SaneIsolate to main isolate

Fixes #17

packages/sane/lib/src/isolate_messages/exception.dart

@@ -0,0 +1,8 @@
+import 'package:sane/src/exceptions.dart';
+import 'package:sane/src/isolate_messages/interface.dart';
+
+class ExceptionResponse implements IsolateResponse {
+  ExceptionResponse({required this.exception});
+
+  final SaneException exception;
+}

packages/sane/lib/src/sane_isolate.dart

@@ -6,6 +6,7 @@ import 'package:sane/src/isolate_messages/cancel.dart';
 import 'package:sane/src/isolate_messages/close.dart';
 import 'package:sane/src/isolate_messages/control_button_option.dart';
 import 'package:sane/src/isolate_messages/control_option.dart';
+import 'package:sane/src/isolate_messages/exception.dart';
 import 'package:sane/src/isolate_messages/exit.dart';
 import 'package:sane/src/isolate_messages/get_all_option_descriptors.dart';
 import 'package:sane/src/isolate_messages/get_devices.dart';
@@ -57,6 +58,10 @@ class SaneIsolate implements Sane {
     final response = await replyPort.first;
     replyPort.close();
 
+    if (response is ExceptionResponse) {
+      throw response.exception;
+    }
+
     return response;
   }
 
@@ -300,9 +305,14 @@ void _isolateEntryPoint(_IsolateEntryPointArgs args) {
   isolateReceivePort.listen((envellope) async {
     envellope = envellope as _IsolateMessageEnveloppe;
 
-    envellope.replyPort.send(
-      await envellope.message.handle(sane),
-    );
+    late IsolateResponse response;
+    try {
+      response = await envellope.message.handle(sane);
+    } on SaneException catch (e) {
+      response = ExceptionResponse(exception: e);
+    }
+
+    envellope.replyPort.send(response);
   });
 }