editor/fold: fix void-variable hs-block-start-regexp
editor/fold: fix void-variable hs-block-start-regexp

Which will happen if +fold/next is called before hideshow is loaded.

hlissner/doom-emacs,hlissner/doom-emacs,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom,hlissner/.emacs.d,hlissner/.emacs.d