(node): org-roam-node-at-point: don't error in non-org buffers (#2329)

`=' assumes that both objects being compared are numbers. In some
buffers `outline-level' can return nil, so `=' returns an error. `eq'
does not assume this, but does return t when comparing two numbers.

org-roam-node.el

@@ -236,11 +236,10 @@ populated."
         (t (org-with-wide-buffer
             (while (not (or (org-roam-db-node-p)
                             (bobp)
-                            ;; Handle case where top-level is a heading
+                            (eq (funcall outline-level)
-                            (= (funcall outline-level)
+                                (save-excursion
-                               (save-excursion
+                                  (org-roam-up-heading-or-point-min)
-                                 (org-roam-up-heading-or-point-min)
+                                  (funcall outline-level)))))
-                                 (funcall outline-level)))))
               (org-roam-up-heading-or-point-min))
             (when-let ((id (org-id-get)))
               (org-roam-populate