Back-end JVM: more accurate handling of when expressions with Unit result #KT-12192 Fixed

compiler/testData/codegen/bytecodeText/when/exhaustiveWhenUnitStatement.kt

@@ -0,0 +1,18 @@
+enum class AccessMode { READ, WRITE, EXECUTE }
+
+fun whenExpr(access: AccessMode) {
+    when (access) {
+        AccessMode.READ -> {}
+        AccessMode.WRITE -> {}
+        AccessMode.EXECUTE -> {}
+    }
+}
+
+fun box(): String {
+    whenExpr(AccessMode.EXECUTE)
+    return "OK"
+}
+
+// 1 TABLESWITCH
+// 0 LOOKUPSWITCH
+// 0 ATHROW