如果满足包头的解析，请返回True，并且递增整个包头的长度到Position，然后赋值BodyLength
如果返回，意味着缓存剩余数据，此时如果仅仅是因为长度不足，则不必修改其他。
bool IBigUnfixedHeaderRequestInfo.OnParsingHeader<TReader>(
ref TReader reader
)
where TReader : IBytesReader
Private Function OnParsingHeader(Of TReader As IBytesReader) (
ByRef reader As TReader
) As Boolean Implements IBigUnfixedHeaderRequestInfo.OnParsingHeaderprivate abstract OnParsingHeader :
reader : 'TReader byref -> bool when 'TReader : IBytesReader
private override OnParsingHeader :
reader : 'TReader byref -> bool when 'TReader : IBytesReader[缺少 "M:TouchSocket.Http.WebSockets.WSDataFrame.TouchSocket#Core#IBigUnfixedHeaderRequestInfo#OnParsingHeader``1(``0@)" 的 <typeparam name="TReader"/> 文档]