Fix for a problem with smart cast impossible in a situation when it's not needed. A test for KT-3572. #KT-3572 Fixed.

compiler/testData/diagnostics/tests/smartCasts/kt3572.kt

@@ -0,0 +1,17 @@
+trait Printer {
+    fun print()
+}
+
+class OKPrinter : Printer {
+    override fun print() {  }
+}
+
+class MyClass(var printer: Printer)
+
+
+fun main(m: MyClass) {
+    if (m.printer is OKPrinter) {
+        // We do not need smart cast here, so we should not get SMARTCAST_IMPOSSIBLE
+        m.printer.print()
+    }
+}