Fix "Narrowing src/ file breaks xref"

* lisp/emacs-lisp/find-func.el (find-function-C-source):
Look outside of the current narrowing as well (bug#80749).

lisp/emacs-lisp/find-func.el

@@ -302,6 +302,7 @@ TYPE should be nil to find a function, or `defvar' to find a variable."
 		      (indirect-function
 		       (find-function-advised-original fun-or-var)))))
   (with-current-buffer (find-file-noselect file)
+    (without-restriction
       (goto-char (point-min))
       (unless (re-search-forward
 	       (if type
@@ -313,7 +314,7 @@ TYPE should be nil to find a function, or `defvar' to find a variable."
 		         "\""))
 	       nil t)
         (error "Can't find source for %s" fun-or-var))
-    (cons (current-buffer) (match-beginning 0))))
+      (cons (current-buffer) (match-beginning 0)))))
 
 ;;;###autoload
 (defun find-library (library)