xdg-mime: make sure the target directories exist

Before the profile commands would not run if a single package is
installed since `buildEnv` will produce a symlink directly to that
package. By adding this dummy package we ensure that a real directory
will be generated.

Fixes #1392

modules/misc/xdg-mime.nix

@@ -27,6 +27,11 @@ in {
     home.packages = [
       # Explicitly install package to provide basic mime types.
       pkgs.shared-mime-info
+
+      # Make sure the target directories will be real directories.
+      (pkgs.runCommandLocal "dummy-xdg-mime-dirs" { } ''
+        mkdir -p $out/share/{applications,mime/packages}
+      '')
     ];
 
     home.extraProfileCommands = ''