[bgw-gui] FileDialog extension filters not showing specified filetypes on opening

[smilefx]

Describe the bug
The FileDialog extension filters do not work as intended. Saving a file works fine (including setting the extensionFilters). Chosing to use mode = FileDialogMode.OPEN_FILE however does not display any files (not even ones matching the filter).

To Reproduce
Steps to reproduce the behavior:

BoardGameApplication.showFileDialog(
    FileDialog(
        title = "Load file",
        mode = FileDialogMode.OPEN_FILE,
        extensionFilters = listOf(ExtensionFilter("Proprietary File Format", "pff"))
    )
)

Alternatively using a .pff in the filter doesn't work either:

BoardGameApplication.showFileDialog(
    FileDialog(
        title = "Load file",
        mode = FileDialogMode.OPEN_FILE,
        extensionFilters = listOf(ExtensionFilter("Proprietary File Format", ".pff"))
    )
)

Expected behavior
Should list all files matching the given extension filter and not only folders.

Please complete the following information:

• OS: Windows 10
• Java version: OpenJDK 15