[Attributor] Fix AAExecutionDomain returning true on invalid states

This patch fixes a problem with the AAExecutionDomain attributor not
checking if it is in a valid state. This can cause it to incorrectly
return that a block is executed in a single threaded context after the
attributor failed for any reason.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D103186