[SCEV] Fix the movement of insertion point in expander. PR35406.

We cannot move the insertion point to header if SCEV contains div/rem
operations due to they may go over check for zero denominator.

Reviewers: sanjoy, mkazantsev, sebpop
Reviewed By: sebpop
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D41229

llvm-svn: 320789