repo/http: fix client is not informed to provide credentials
repo/http: fix client is not informed to provide credentials

When Git client has cached credentials for a site, missing response
header 'WWW-Authenticate: Basic realm="."' will result in Git client
does not prompt user to input credentials again but plain error
message and halts push/pull process.

mukaiu/gogs,xaionaro/gogs,cgars/gogs,xaionaro/gogs,dancewing/gogs,linquize/gogs,ForxaCoLab/forxa,dancewing/gogs,pikacloud/pikacode,pikacloud/pikacode,wangjild/gogs,ForxaCoLab/forxa,wangjild/gogs,mukaiu/gogs,chriswatt/gogs,linquize/gogs,mukaiu/gogs,dancewing/gogs,pikacloud/pikacode,gogits/gogs,cgars/gogs,gogits/gogs,xaionaro/gogs,gogits/gogs,chriswatt/gogs,cgars/gogs,linquize/gogs,wangjild/gogs,chriswatt/gogs,dancewing/gogs,ForxaCoLab/forxa