Description of the Issue

When using the User Defined Language dialog (v2.1.0.12) and choosing to Export, the Save As dialog says "Save as type: UDL (*.xml)" but the saved file defaults to the .txt extension. This file is then not visible from the Import dialog.

This is a minor issue, but should also be an easy issue to correct.

Steps to Reproduce the Issue

1. From the Language menu select "Define your language..."
2. From the User Defined Language dialog pick "Export..."
3. From the Save As dialog enter a filename like "test" and click the Save button.
4. Click the "Import..." button. Notice that "test" is not listed. This dialog only shows .xml files.
5. If you use Windows Explorer to look in the folder the file is named "test.txt" instead of "test.xml"

Expected Behavior

If I don't provide a file extension, I expect it to apply the extension ".xml" to the saved file.

Actual Behavior

It uses ".txt" as the default extension even though UDL files need to be ".xml"

Debug Information

Notepad++ v7.5.3 (32-bit)
Build time : Dec 5 2017 - 10:45:46
Path : C:\Program Files (x86)\Notepad++\notepad++.exe
Admin mode : ON
Local Conf mode : OFF
OS : Windows 7 (64-bit)
Plugins : ComparePlugin.dll DSpellCheck.dll JSLintNpp.dll JSMinNPP.dll mimeTools.dll NppConverter.dll NppExport.dll NppTextFX.dll PluginManager.dll PoorMansTSqlFormatterNppPlugin.dll sqlFormat.dll Tidy2.dll