bump base/blitbuffer.c: small optimisation
bump base/blitbuffer.c: small optimisation

NiLuJe/koreader,Markismus/koreader,poire-z/koreader,koreader/koreader,mwoz123/koreader,koreader/koreader,mihailim/koreader,Frenzie/koreader,NiLuJe/koreader,Hzj-jie/koreader,Frenzie/koreader,houqp/koreader,poire-z/koreader,pazos/koreader