[DAGCombine] Fix splitting indexed loads in ForwardStoreValueToDirectLoad()
In DAGCombiner::visitLOAD() we perform some checks before breaking up an indexed
load. However, we don't do the same checking in ForwardStoreValueToDirectLoad()
which can lead to failures later during combining
This patch just adds the same checks to this function as well.
Differential revision: https://reviews.llvm.org/D76778