[LICM] Fix a small oversight introduced in r256763

[LICM] Fix a small oversight introduced in r256763

r256763 had promoteLoopAccessesToScalars check for the existence of a
catchswitch when the exit blocks were populated but
promoteLoopAccessesToScalars may be called with a prepopulated set of
exit blocks which would also need to be checked.

This fixes PR26019.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256788 91177308-0d34-0410-b5e6-96231b3b80d8