[DAGCombine] Fix splitting indexed loads in ForwardStoreValueToDirectLoad()

[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
(see: https://bugs.llvm.org/show_bug.cgi?id=45301).

This patch just adds the same checks to this function as well.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=45301

Differential revision: https://reviews.llvm.org/D76778