Branch returned although one of the next states simplifies to #bottom

[jberthold]

On slack, Petar reported a problem where a branch result returned by (both kore-rpc and) kore-rpc-booster contains two next-states, but one of them simplifies to #Bottom with an isolated simplify request.
This is caused by kore-rpc execution not discovering the #Bottom-ness of this state, otherwise execution would continue.

Observed behaviour:

• Execution stops and a Branching result is returned. One of the states in next-states simplifies to #Bottom in a subsequent simplify request.

Expected behaviour:

• Execution should continue with the non-bottom alternative of the branch.

• to protect against this behaviour in kore-rpc-booster, modify the postExecSimplify mechanism to detect this case and continue execution.
• reproduce this result with kore-rpc and investigate why the bottom state is not found

[jberthold]

There were once known issues with spurious branches at depth 0 in kore-rpc earlier, so this behaviour should be tested this with a noop step before the branch, too. The reason appears to be that the simplifier is not called for branch results at depth 0. This should be investigated.

[jberthold]

I have confirmed with tests that in this case, it makes no difference whether kore-rpc has performed an execution step before the bogus Branching result is obtained.