fix(macos/dialog): avoid setting empty `default_path` (#9784)

closes #7566

ref: https://github.com/tauri-apps/tauri/issues/4065
ref: https://github.com/tauri-apps/tauri/pull/4028
ref: https://github.com/tauri-apps/tauri/issues/9762

.changes/macos-dialog-crash-default-path-empty.md

@@ -0,0 +1,5 @@
+---
+"tauri": "patch:bug"
+---
+
+Fix dialog crash on macOS when the `default_path` value is empty.

core/tauri/src/endpoints/dialog.rs

@@ -301,6 +301,10 @@ fn set_default_path(
   mut dialog_builder: FileDialogBuilder,
   default_path: PathBuf,
 ) -> FileDialogBuilder {
+  if default_path.as_os_str().is_empty() {
+    return dialog_builder;
+  }
+
   // 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() {