[ScalarEvolution] Add an additional bailout to avoid NOT of pointer.

It's possible in some cases for the LHS to be a pointer where the RHS is not. This isn't directly possible for an icmp, but the analysis mixes up operands of different icmp expressions in some cases.

This does not include a test case as the smallest reduced case we've managed is extremely fragile and unlikely to test anything meaningful in the long term.

Also add an assertion to getNotSCEV() to make tracking down this sort of issue a bit easier in the future.

Fixes https://bugs.llvm.org/show_bug.cgi?id=51787 .

Differential Revision: https://reviews.llvm.org/D109546