Relax rules about inferring to Nothing for special calls

#KT-37388 Fixed
 #KT-38427 Fixed
 #KT-39953 Fixed
 #KT-38899 Fixed

compiler/testData/diagnostics/tests/when/kt9972.kt

@@ -11,12 +11,12 @@
  */
 
 fun test1(): Int {
-    val x: String = <!NI;TYPE_MISMATCH!>if (true) {
+    val x: String = if (true) <!NI;TYPE_MISMATCH!>{
         when {
             true -> <!OI;TYPE_MISMATCH!>Any()<!>
             else -> <!OI;NULL_FOR_NONNULL_TYPE!>null<!>
         }
-    } else ""<!>
+    }<!> else ""
     return x.hashCode()
 }