[Test] Add test for KT-40851

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/initializationInUnreachableCode.kt

@@ -0,0 +1,13 @@
+// COMPARE_WITH_LIGHT_TREE
+// ISSUE: KT-40851
+
+fun error(): Nothing = throw Exception()
+
+class Some() {
+    <!MUST_BE_INITIALIZED_OR_BE_ABSTRACT!>var x: Int<!>
+    val y: Int = error()
+
+    init {
+        x = 1;
+    }
+}