Fix `start is undefined`.
Fix `start is undefined`.

mysticatea/acorn,btmills/acorn,MarcelGerber/acorn,TimothyGu/acorn,marijnh/acorn,marijnh/acorn,happibum/acorn,ajaxorg/acorn,ternjs/acorn,Rich-Harris/acorn,mysticatea/acorn,mathiasbynens/acorn,btmills/acorn,happibum/acorn,Rich-Harris/acorn,mysticatea/acorn,btmills/acorn,TimothyGu/acorn,marijnh/acorn,ternjs/acorn,TimothyGu/acorn,MarcelGerber/acorn,MarcelGerber/acorn,mathiasbynens/acorn,ajaxorg/acorn,ternjs/acorn,Rich-Harris/acorn,mathiasbynens/acorn,ajaxorg/acorn,happibum/acorn