Prevent E_NOTICE when session already started
Prevent E_NOTICE when session already started

Using strict equality.  Patching release branch.
prashantquestionpro/Slim,somjit2514/basic,luizdeangeli/Slim,feryardiant/slim,pedro2555/Slim,samsonasik/Slim,jenalgit/Slim,Sam-Burns/Slim,danielgsims/Slim,julianromera/Slim,slimphp/Slim,huang53798584/Slim,gabriel403/Slim,makelivedotnet/Slim,ColourboxDevelopment/Slim,fredemmott/Slim,tempbottle/Slim,kutanari/Slim,iinux/Slim,fsciuti/Slim,anuradhaedirisuriya/Slim,abfadel/Slim,1nv4d3r5/Slim,iinux/Slim,jaapverloop/Slim,mmauri04/Slim,gencer/Slim,opengeek/Slim,dopesong/Slim,FraGoTe/Slim,umiyosh/SlimDocDemo,geggleto/Slim,bact197736/Slim,Alex2147483647/Slim,beealone/Slim,kanellov/Slim,chezzy/Slim,dkarvounaris/Slim,jeremykendall/Slim,juliangut/Slim,moufmouf/Slim,tanuck/Slim,nslod/Slim,zither/Slim,cesarmarinhorj/Slim,JoeBengalen/Slim,lmcro/Slim,szulilin/Slim,designermonkey/Slim,EhteshamMehmood/Slim,xMolchy/Slim,umiyosh/SlimDocDemo,AndrewCarterUK/Slim,shameerc/Slim,AI0day/slim,mnapoli/Slim,silentworks/Slim,swantrace/Slim-1,iinux/Slim,andresvidal/Slim,RealSelf/Slim,joelgarciajr84/Slim,greevex/Slim,asaokamei/Slim,foxyantho/Slim,Vinniefern99/Slim,akrabat/Slim,lornajane/Slim,xiuchanghu/Slim,lcp0578/Slim,lekoaf/Slim,taohaolong/Slim,matheusgomes17/Slim,pine3ree/Slim