DependenceAnalysis: Don't crash if there is no constant operand.

This makes the code match the comments. Resolves a crash in loop idiom (PR14219).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167110 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed