New J2K: consider empty/singleton children list when comparing trees in default arguments conversion

nj2k/src/org/jetbrains/kotlin/nj2k/conversions/DefaultArgumentsConversion.kt

@@ -145,11 +145,11 @@ class DefaultArgumentsConversion(context: NewJ2kConverterContext) : RecursiveApp
                                 child1 as JKElement,
                                 child2 as JKElement
                             )
-                        }.reduce(Boolean::and)
+                        }.fold(true, Boolean::and)
                     }
                     else -> false
                 }
-            }.reduce(Boolean::and)
+            }.fold(true, Boolean::and)
         } else false
     }