When opening a "Save" file dialog with a default output file name,
OSX file dialog strips the provided extension and replaces it
with the default extension. This causes issues with a custom
file output template, where a non-default file extension is specified.
This commit changes the function to generate file dialog templates
so that if a default extension is provided, it is emitted
as first into the extension template.
Fixes Post Processing passes wrong name #7190
e7cc12b2c9