ConvertSwitchToIfIntention: fix processing of empty blocks

IDEA-205137 `Replace Switch with If` produce exceptions
IDEA-205122 Unwrap switch fails with exception

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/switchDefault/beforeRuleEmpty.java

@@ -0,0 +1,11 @@
+// "Unwrap 'switch'" "true"
+public class One {
+  void n() {
+    if (true) {
+      swit<caret>ch (0) {
+        default -> {
+        }
+      }
+    }
+  }
+}