puredata: fix pd-gui by providing tk path

Prior to this commit, the `pd-gui` command fails to launch with:

`pd-gui.tcl: line 3: exec: wish: not found`

This is because we were only wrapping `pd` with the `tk` path, but not
`pd-gui`.

This also resulted in the puredata desktop shortcut failing, as it
attempts to invoke `pd-gui` directly.

This commit fixes these issues by also wrapping `pd-gui` with the `tk`
path.

pkgs/applications/audio/puredata/default.nix

@@ -62,6 +62,7 @@ stdenv.mkDerivation rec {
 
   postInstall = ''
     wrapProgram $out/bin/pd --prefix PATH : ${lib.makeBinPath [ tk ]}
+    wrapProgram $out/bin/pd-gui --prefix PATH : ${lib.makeBinPath [ tk ]}
   '';
 
   meta = with lib; {