Make sure the 'modus-themes-theme' reads the updated palette value

Otherwise palette overrides do not work intended. This was a
regression caused by commit 085ee06.

Thanks to chainedghost for reporting the bug in issue 161:
<https://github.com/protesilaos/modus-themes/issues/161>.

doc/modus-themes.info

@@ -6121,9 +6121,9 @@ Ideas and user feedback
      Sharf, Utkarsh Singh, Vincent Foley, Zoltan Kiraly.  As well as
      users: Ben, CsBigDataHub1, Emacs Contrib, Eugene, Fourchaux,
      Fredrik, Moesasji, Nick, Summer Emacs, TheBlob42, TitusMu, Trey,
-     bepolymathe, bit9tream, bangedorrunt, case-lambda, derek-upham,
-     doolio, fleimgruber, gitrj95, iSeeU, jixiuf, ltmsyvag, okamsn,
-     pedro-nonfree, pRot0ta1p, shipmints, soaringbird, tumashu,
+     bepolymathe, bit9tream, bangedorrunt, case-lambda, chainedghost,
+     derek-upham, doolio, fleimgruber, gitrj95, iSeeU, jixiuf, ltmsyvag,
+     okamsn, pedro-nonfree, pRot0ta1p, shipmints, soaringbird, tumashu,
      wakamenod.
 
 Packaging
@@ -6943,11 +6943,11 @@ Node: Sources of the themes254309
 Node: Issues you can help with255205
 Node: Patches require copyright assignment to the FSF256597
 Node: Acknowledgements258819
-Node: GNU Free Documentation License263288
-Node: Indices288451
-Node: Function index288630
-Node: Variable index291740
-Node: Concept index295948
+Node: GNU Free Documentation License263302
+Node: Indices288465
+Node: Function index288644
+Node: Variable index291754
+Node: Concept index295962
 
 End Tag Table
 

doc/modus-themes.org

@@ -5947,9 +5947,9 @@ The Modus themes are a collective effort.  Every bit of work matters.
   Zoltan Kiraly. As well as users: Ben, CsBigDataHub1, Emacs Contrib,
   Eugene, Fourchaux, Fredrik, Moesasji, Nick, Summer Emacs, TheBlob42,
   TitusMu, Trey, bepolymathe, bit9tream, bangedorrunt, case-lambda,
-  derek-upham, doolio, fleimgruber, gitrj95, iSeeU, jixiuf, ltmsyvag,
-  okamsn, pedro-nonfree, pRot0ta1p, shipmints, soaringbird, tumashu,
-  wakamenod.
+  chainedghost, derek-upham, doolio, fleimgruber, gitrj95, iSeeU,
+  jixiuf, ltmsyvag, okamsn, pedro-nonfree, pRot0ta1p, shipmints,
+  soaringbird, tumashu, wakamenod.
 
 + Packaging :: Basil L.{{{space()}}} Contovounesios, Eli Zaretskii,
   Glenn Morris, Mauro Aranda, Richard Stallman, Stefan Kangas (core

modus-themes.el

@@ -7298,12 +7298,11 @@ Consult the manual for details on how to build a theme on top of the
     (let ((palette (modus-themes--get-theme-palette-subr name :with-overrides :with-user-palette)))
       (eval
        `(let* ((c '((class color) (min-colors 256)))
+               (palette (modus-themes--get-theme-palette-subr ',name :with-overrides :with-user-palette))
                ,@(mapcar
-                  (pcase-lambda (`(,name ,value))
-                    (pcase value
-                      ('unspecified (list name ''unspecified))
-                      ((pred symbolp) (list name `(modus-themes--retrieve-palette-value ',name ',palette)))
-                      ((pred stringp) (list name value))))
+                  (lambda (entry)
+                    (let ((name (car entry)))
+                      (list name `(modus-themes--retrieve-palette-value ',name palette))))
                   palette))
           (custom-theme-set-faces
            ',name