MdeModulePkg:DxeHttpLib: Add checks in HttpGenRequestMessage API
    
    HttpGenRequestMessage assumes that HTTP message would always
    contain a request-line, headers and an optional message body.
    However, subsequent to a HTTP PUT/POST request, HTTP requests
    would contain just the message body. This patch supports
    creation of such request messages with additional checks.
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Hegde, Nagaraj P <nagaraj-p.hegde@hpe.com>
    Reviewed-By: Wu Jiaxin <jiaxin.wu@intel.com>
    Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>