Review request for JDK-8078414: Don't create impossible converters for ScriptObjectMirror

[Attila Szegedi]

Please review JDK-8078414 "Don't create impossible converters for 
ScriptObjectMirror" at <http://cr.openjdk.java.net/~attila/8078414/webrev.00> 
for <https://bugs.openjdk.java.net/browse/JDK-8078414>

Thanks,
  Attila.