KT-9835 Completion thinks receiver is nullable when it is not

#KT-9835 Fixed

idea/idea-completion/testData/basic/java/syntheticExtensions/InGenericClass.kt

@@ -2,9 +2,14 @@ fun foo(klass: Class<*>) {
     klass.<caret>
 }
 
+fun <T> Class<T>.extFun(): Class<in T> = TODO()
+
 // EXIST: simpleName
 // ABSENT: getSimpleName
 // EXIST: enclosingClass
 // ABSENT: getEnclosingClass
 // EXIST: annotations
 // ABSENT: getAnnotations
+// EXIST: superclass
+// ABSENT: getSuperclass
+// EXIST: extFun