[Refactoring] Don't transform unrelated switches

We were missing a `return` here to ignore any
switch statements that don't have anything to do
with the error handling.

Author: hamishknight

lib/IDE/Refactoring.cpp

@@ -4680,6 +4680,7 @@ struct CallbackClassifier {
   void classifySwitch(SwitchStmt *SS) {
     if (!IsResultParam || singleSwitchSubject(SS) != ErrParam) {
       CurrentBlock->addNode(SS);
+      return;
     }
 
     for (auto *CS : SS->getCases()) {

test/refactoring/ConvertAsync/convert_result.swift

@@ -322,3 +322,25 @@ voidAndErrorResult { res in
 }
 // VOID-AND-ERROR-RESULT-CALL: {{^}}try await voidAndErrorResult()
 // VOID-AND-ERROR-RESULT-CALL: {{^}}print(<#res#>)
+
+// Make sure we ignore an unrelated switch.
+// RUN: %refactor -convert-call-to-async-alternative -dump-text -source-filename %s -pos=%(line+1):1 | %FileCheck -check-prefix=IGNORE-UNRELATED %s
+simple { res in
+  print("before")
+  switch Bool.random() {
+  case true:
+    break
+  case false:
+    break
+  }
+  print("after")
+}
+// IGNORE-UNRELATED:      let res = try await simple()
+// IGNORE-UNRELATED-NEXT: print("before")
+// IGNORE-UNRELATED-NEXT: switch Bool.random() {
+// IGNORE-UNRELATED-NEXT:  case true:
+// IGNORE-UNRELATED-NEXT:  {{^}} break{{$}}
+// IGNORE-UNRELATED-NEXT:  case false:
+// IGNORE-UNRELATED-NEXT:  {{^}} break{{$}}
+// IGNORE-UNRELATED-NEXT:  }
+// IGNORE-UNRELATED-NEXT: print("after")