Skip write-only formats (#308)

PALM and PDF are write-only formats by PIL, these cannot be opened.

Also move SVG out from the loop to avoid adding it multiple times.

Reference:
https://pillow.readthedocs.io/en/stable/handbook/image-file-formats.html#write-only-formats

cartridges/details_dialog.py

@@ -89,8 +89,11 @@ class DetailsDialog(Adw.Dialog):
             self.apply_button.set_label(_("Add"))
 
         image_filter = Gtk.FileFilter(name=_("Images"))
-        for extension in Image.registered_extensions():
+
+        # .palm and .pdf are write-only
+        for extension in set(Image.registered_extensions()) - {".palm", ".pdf"}:
             image_filter.add_suffix(extension[1:])
+
         image_filter.add_suffix("svg")  # Gdk.Texture supports .svg but PIL doesn't
 
         image_filters = Gio.ListStore.new(Gtk.FileFilter)