x?.y != null and x?.call() != null provoke now x != null, a set of tests #KT-2127 Fixed

compiler/testData/diagnostics/tests/smartCasts/safecalls/propertyChain.kt

@@ -9,6 +9,6 @@ fun foo(y: MyClass?): Int {
 }
 fun bar(y: MyClass?) {
     y?.x!!.length
-    // !! is necessary here
-    y!!.x
+    // !! is NOT necessary here, because y?.x != null
+    y<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>.x
 }