[V3] Windows: fix(application): handle error and type assertion in save file dialog

docs/src/content/docs/changelog.mdx

@@ -32,6 +32,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Add distribution-specific build dependencies for Linux by @leaanthony in [PR](https://github.com/wailsapp/wails/pull/4345)
   - Added bindings guide by @atterpac in [PR](https://github.com/wailsapp/wails/pull/4404)
 
+### Fixed
+- Fixed panic when closing or cancelling a `SaveFileDialog` on windows. Fixed in [PR](https://github.com/wailsapp/wails/pull/4284) by @hkhere
+
 ## v3.0.0-alpha.10 - 2025-07-06
 
 ### Breaking Changes

v3/internal/go-common-file-dialog/cfd/vtblCommonFunc.go

@@ -4,10 +4,11 @@ package cfd
 
 import (
 	"fmt"
-	"github.com/go-ole/go-ole"
 	"strings"
 	"syscall"
 	"unsafe"
+
+	"github.com/go-ole/go-ole"
 )
 
 func hresultToError(hr uintptr) error {
@@ -168,7 +169,7 @@ func (vtbl *iFileDialogVtbl) getResultString(objPtr unsafe.Pointer) (string, err
 		return "", err
 	}
 	if shellItem == nil {
-		return "", fmt.Errorf("shellItem is nil")
+		return "", ErrorCancelled
 	}
 	defer shellItem.vtbl.release(unsafe.Pointer(shellItem))
 	return shellItem.vtbl.getDisplayName(unsafe.Pointer(shellItem))

v3/pkg/application/dialogs_windows.go

@@ -196,9 +196,16 @@ func (m *windowSaveFileDialog) show() (chan string, error) {
 		func() (cfd.Dialog, error) {
 			return cfd.NewSaveFileDialog(config)
 		}, false)
+	if err != nil {
+		close(files)
+		return files, err
+	}
 	go func() {
 		defer handlePanic()
-		files <- result.(string)
+		f, ok := result.(string)
+		if ok {
+			files <- f
+		}
 		close(files)
 	}()
 	return files, err