Bring back init of instance flags in non-readWrite mode (C++, C#)

(fix regression from d1f16dd)

Author: generalmimon

shared/src/main/scala/io/kaitai/struct/ClassCompiler.scala

@@ -140,9 +140,9 @@ class ClassCompiler(
       curClass.params
     )
     compileInit(curClass)
+    curClass.instances.foreach { case (instName, _) => lang.instanceClear(instName) }
     if (config.readWrite) {
       curClass.instances.foreach { case (instName, instSpec) =>
-        lang.instanceClear(instName)
         instSpec match {
           case _: ParseInstanceSpec =>
             lang.instanceWriteFlagInit(instName)