Avoid repeatedly evaluating subexpressions when checking for unsequenced
operations in the case where evaluating a subexpression fails. No functionality
change, but test/Sema/many-logical-ops.c gets ~100x faster with this change.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184489 91177308-0d34-0410-b5e6-96231b3b80d8