fix(core/dialog): reconstruct path using appropriate separator, closes #8074 (#8408)

* fix(core/dialog): reconstruct path using appropraite separator, closes #8074

* Update dialog-window-forward-slash.md

* Update dialog.rs

* Update core/tauri/src/endpoints/dialog.rs

---------

Co-authored-by: Lucas Fernandes Nogueira <lucas@tauri.app>

.changes/dialog-window-forward-slash.md

@@ -0,0 +1,5 @@
+---
+'tauri': 'patch:bug'
+---
+
+On Windows, fix `open` dialog `defaultPath`, when invoked from JS, not working if the path uses forward slash (`/`)

core/tauri/src/endpoints/dialog.rs

@@ -301,6 +301,8 @@ fn set_default_path(
   mut dialog_builder: FileDialogBuilder,
   default_path: PathBuf,
 ) -> FileDialogBuilder {
+  // we need to adjust the separator on Windows: https://github.com/tauri-apps/tauri/issues/8074
+  let default_path: PathBuf = default_path.components().collect();
   if default_path.is_file() || !default_path.exists() {
     if let (Some(parent), Some(file_name)) = (default_path.parent(), default_path.file_name()) {
       if parent.components().count() > 0 {