wrapAndApplyHeader doesnt respect constant fields in the MessageHeader

[kdkavanagh]

I don't have a need for schemaID in the MessageHeader and have set it to a constant in the XML. This runs through the sbe-tool without complaints, however the generated wrapAndApplyHeader methods still try to apply the schemaID, ignoring the fact that it is a constant.

XML:

    <composite name="messageHeader" description="Message identifiers and length of message root">
        <type name="msgSize" primitiveType="uint16"/>
        <type name="templateId" primitiveType="uint16"/>
        <type name="version" primitiveType="uint16"/>
        <type name="blockLength" primitiveType="uint16"/>
        <type name="schemaId" primitiveType="uint16" presence="constant">1</type>
    </composite>

Generated java:

    public TestFixedWidthMessageEncoder wrapAndApplyHeader(
        final MutableDirectBuffer buffer, final int offset, final MessageHeaderEncoder headerEncoder)
    {
        headerEncoder
            .wrap(buffer, offset)
            .blockLength(BLOCK_LENGTH)
            .templateId(TEMPLATE_ID)
            .schemaId(SCHEMA_ID)
            .version(SCHEMA_VERSION);

        return wrap(buffer, offset + MessageHeaderEncoder.ENCODED_LENGTH);
    }

[mjpt777]

This will break the spec in that the header has to have those minimum 4 fields on the wire.