Minor, add test for obsolete issue

#KT-3587 Obsolete

compiler/testData/codegen/box/regressions/kt3587.kt

@@ -0,0 +1,10 @@
+open class Variable {
+    val lightVar: LightVariable = if (this is LightVariable) this else LightVariable()
+}
+
+class LightVariable() : Variable()
+
+fun box(): String {
+    Variable()
+    return "OK"
+}