Fix oversight of SetDismissText before showing

CHANGELOG.md

@@ -3,6 +3,10 @@
 This file lists the main changes with each version of the Fyne toolkit.
 More detailed release notes can be found on the [releases page](https://github.com/fyne-io/fyne/releases). 
 
+## 2.1.4 - Ongoing
+
+* FolderOpenDialog SetDismissText is ineffective (#2830)
+
 ## 2.1.3 - 24 February 2021
 
 ### Fixed

dialog/file.go

@@ -594,6 +594,7 @@ func (f *FileDialog) Hide() {
 
 // SetDismissText allows custom text to be set in the confirmation button
 func (f *FileDialog) SetDismissText(label string) {
+	f.dismissText = label
 	if f.dialog == nil {
 		return
 	}

dialog/file_test.go

@@ -431,6 +431,7 @@ func TestView(t *testing.T) {
 		assert.Nil(t, reader)
 	}, win)
 
+	dlg.SetDismissText("Dismiss")
 	dlg.Show()
 
 	popup := win.Canvas().Overlays().Top().(*widget.PopUp)
@@ -470,6 +471,9 @@ func TestView(t *testing.T) {
 	// toggleViewButton should reflect to what it will do (change to a list view).
 	assert.Equal(t, "", toggleViewButton.Text)
 	assert.Equal(t, theme.ListIcon(), toggleViewButton.Icon)
+
+	dismiss := ui.Objects[2].(*fyne.Container).Objects[0].(*fyne.Container).Objects[0].(*widget.Button)
+	assert.Equal(t, "Dismiss", dismiss.Text)
 }
 
 func TestFileFavorites(t *testing.T) {