[llvm] [llvm][UnifyLoopExits] Avoid optimization if no exit block is found (PR #165343)

[Dmitry Sidorov via llvm-commits]

================
@@ -299,6 +299,8 @@ std::pair<BasicBlock *, bool> ControlFlowHub::finalize(
       Outgoing.insert(Succ1);
   }
 
+  assert(Outgoing.size());
----------------
MrSidims wrote:

nitpick:
```suggestion
  assert(Outgoing.size() && "No outgoing edges from a loop");
```

https://github.com/llvm/llvm-project/pull/165343