Regexp::Parse: fix memory access past end of input
Regexp::Parse: fix memory access past end of input

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R=rsc
CC=re2-dev
http://codereview.appspot.com/4121047

dragonkid/re2,lamuguo/re2,pombreda/re2,PiRSquared17/re2,lamuguo/re2,PiRSquared17/re2,zeusdeux/re2,zeusdeux/re2,pombreda/re2,tst2005googlecode/re2,Distrotech/re2,tst2005googlecode/re2,Distrotech/re2,tst2005googlecode/re2,dragonkid/re2,dragonkid/re2,zeusdeux/re2,nelhage/re2,Distrotech/re2,nelhage/re2,nelhage/re2,pombreda/re2,tst2005googlecode/re2,nelhage/re2,PiRSquared17/re2,nelhage/re2,Distrotech/re2,dragonkid/re2,nelhage/re2,PiRSquared17/re2,lamuguo/re2,lamuguo/re2,tst2005googlecode/re2,zeusdeux/re2,zeusdeux/re2,PiRSquared17/re2,dragonkid/re2,pombreda/re2,pombreda/re2,Distrotech/re2,lamuguo/re2