[loop-region] Add in an assert that we should always have a block result for getRegionForNonLocalSuccessors. NFC.
[loop-region] Add in an assert that we should always have a block result for getRegionForNonLocalSuccessors. NFC.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift