pp--insert-lisp: Don't bug out on certain forms at beginning of buffer

* pp.el (pp--insert): Check if point is in beginning of buffer before
calling `looking-back' (bug#55677).

lisp/emacs-lisp/pp.el

@@ -382,7 +382,7 @@ Use the `pp-max-width' variable to control the desired line length."
         (when (> (current-column) (pp--max-width))
           (condition-case ()
               (backward-up-list 1)
-            (:success (when (looking-back " " 2)
+            (:success (when (and (not (bobp)) (looking-back " " 2))
                         (insert "\n")))
             (error nil)))))))