Support handling URIs via desktop file (#1044)

When thunar is selected as default application for the Mime Type "inode/directory", it now as well opens "trash://" and other URIs. (Before that change, the next file manager in the List was used for such URIs instead of thunar)

(cherry picked from commit 35cc5923)

thunar.desktop.in.in

@@ -3,7 +3,7 @@ _Name=Thunar File Manager
 _Comment=Browse the filesystem with the file manager
 _GenericName=File Manager
 _Keywords=file manager;explorer;finder;browser;folders;directory;directories;partitions;drives;network;devices;rename;move;copy;delete;permissions;home;trash;
-Exec=thunar %F
+Exec=thunar %U
 Icon=org.xfce.thunar
 Terminal=false
 StartupNotify=true