Copy palette before exporting it

Otherwise its save path gets mangled and it will disappear from the
program.

ChangeLog

@@ -13,6 +13,7 @@ Unreleased Version 2.2.0-pre
  * Fix: Actually pick color when adding a color to the color picker through the color dialog.
  * Feature: Mark window when a chat message is received. On Windows, this makes the icon in the task bar orange. On macOS, it supposedly bounces an icon somewhere. On other platforms it probably does something similar, indicating which window is the one that got a message ready. Thanks Radio for suggesting.
  * Fix: Don't add current color to the palette when creating it. Thanks xxxx for reporting.
+ * Fix: Make exported palettes not start using the exported location to save changes to. Thanks xxxx for reporting.
 
 2023-07-31 Version 2.2.0-beta.6
  * Fix: Don't forget account password when entering a wrong session password.

src/desktop/docks/colorpalette.cpp

@@ -354,7 +354,7 @@ void ColorPaletteDock::exportPalette()
 		tr("GIMP palette (%1)").arg("*.gpl"));
 
 	if(!filename.isEmpty()) {
-		color_widgets::ColorPalette &pal = d->paletteWidget->colorPalette();
+		color_widgets::ColorPalette pal = d->paletteWidget->colorPalette();
 
 		if(!pal.save(filename))
 			QMessageBox::warning(this, tr("Error"), tr("Couldn't save file"));