[SDAG] Fix CombineTo ordering in visitZERO_EXTEND and visitSIGN_EXTEND

Reorder CombineTo Calls to prevent references to stale/deleted SDNodes which caused undue assertions.

Reviewers: dbabokin

Subscribers: aemerson, rengolin, llvm-commits

Differential Revision: https://reviews.llvm.org/D31625

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304460 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed