upgrade flutter file picker

lib/views/messageview.dart

@@ -400,10 +400,11 @@ class _MessageViewState extends State<MessageView> {
     // while awaiting for pickFiles.
     var appstate = Provider.of<AppState>(ctx, listen: false);
     appstate.disableFilePicker = true;
-    FilePickerResult? result = await FilePicker.platform.pickFiles();
+    // currently lockParentWindow only works on Windows...
+    FilePickerResult? result = await FilePicker.platform.pickFiles(lockParentWindow: true);
     appstate.disableFilePicker = false;
-    if (result != null) {
-      File file = File(result.files.first.path);
+    if (result != null && result.files.first.path != null) {
+      File file = File(result.files.first.path!);
       // We have a maximum number of bytes we can represent in terms of
       // a manifest (see : https://git.openprivacy.ca/cwtch.im/cwtch/src/branch/master/protocol/files/manifest.go#L25)
       if (file.lengthSync() <= 10737418240) {

pubspec.lock

@@ -112,14 +112,14 @@ packages:
       name: file_picker
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.0.1"
+    version: "4.3.2"
   file_picker_desktop:
     dependency: "direct main"
     description:
       name: file_picker_desktop
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.1.1"
   flutter:
     dependency: "direct main"
     description: flutter

pubspec.yaml

@@ -41,7 +41,7 @@ dependencies:
   flutter_test:
     sdk: flutter
   scrollable_positioned_list: ^0.2.0-nullsafety.0
-  file_picker: ^4.0.1
+  file_picker: ^4.3.2
   file_picker_desktop: ^1.1.0
   url_launcher: ^6.0.12