Fixed old typo in ScalarEvolution, that caused wrong SCEVs zext operation.
Detailed description is here:
http://llvm.org/bugs/show_bug.cgi?id=18000#c16

For participation in bugfix process special thanks to David Wiberg.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198863 91177308-0d34-0410-b5e6-96231b3b80d8