fix an error caused by 16 band mis-read
fix an error caused by 16 band mis-read

@士豆口 对此亦有贡献

admpub/build-web-application-with-golang,astaxie/build-web-application-with-golang,songqii/build-web-application-with-golang,WangKaimin/build-web-application-with-golang,admpub/build-web-application-with-golang,admpub/build-web-application-with-golang,astaxie/build-web-application-with-golang,faxriddin/build-web-application-with-golang,songqii/build-web-application-with-golang,admpub/build-web-application-with-golang,faxriddin/build-web-application-with-golang,WangKaimin/build-web-application-with-golang,astaxie/build-web-application-with-golang