pggui: Use `get_filename()` if Location is active
pggui: Use `get_filename()` if Location is active

In FileChooserWidget, if the filename entry next to the "Location:" label is visible (active), use the `get_filename()` function. This allows the user to choose the directory by typing it into the filename entry.

khalim19/gimp-plugin-export-layers,khalim19/gimp-plugin-export-layers