[FE 1.0] Check for type mismatch for empty when statements

^KT-47922 Fixed

compiler/testData/diagnostics/tests/when/kt47922.kt

@@ -0,0 +1,21 @@
+// ISSUE: KT-47922
+
+package whencase.castissue
+
+sealed class SealedBase {
+    object Complete : SealedBase()
+}
+
+abstract class NonSealedBase {
+    object Complete : NonSealedBase()
+}
+
+sealed class ToState
+
+val sealedTest: SealedBase.() -> ToState? = {
+    <!TYPE_MISMATCH!><!NON_EXHAUSTIVE_WHEN_STATEMENT!>when<!>(this) {}<!>
+}
+
+val nonSealedTest: NonSealedBase.() -> ToState? = {
+    <!TYPE_MISMATCH!>when(this) {}<!>
+}