KT-4009 Unnecessary attempt to do a smart cast causes an error

#KT-4009 Fixed
  do not add smart casted types for vars to constraint system

compiler/testData/diagnostics/tests/smartCasts/inference/kt4009.kt

@@ -0,0 +1,21 @@
+trait PsiElement {
+    fun getText(): String
+    fun getParent(): PsiElement
+}
+
+trait JetExpression : PsiElement
+
+fun foo1(e: PsiElement) {
+    var current: PsiElement? = e
+    var first = true
+    while (current != null) {
+        if (current is JetExpression && first) {
+            println(current!!.getText()) // error: smart cast not possible. But it's not needed in fact!
+        }
+
+        current = current?.getParent()
+    }
+}
+
+//from library
+fun println(any: Any?) = throw Exception("$any")