Avoid duplicate queries in auth (#827)

Avoid identical making calls to GetUserByID(..) in SignedInUser(..)

modules/auth/auth.go

@@ -69,14 +69,7 @@ func SignedInID(ctx *macaron.Context, sess session.Store) int64 {
 	uid := sess.Get("uid")
 	if uid == nil {
 		return 0
-	}
+	} else if id, ok := uid.(int64); ok {
-	if id, ok := uid.(int64); ok {
-		if _, err := models.GetUserByID(id); err != nil {
-			if !models.IsErrUserNotExist(err) {
-				log.Error(4, "GetUserById: %v", err)
-			}
-			return 0
-		}
 		return id
 	}
 	return 0
@@ -89,9 +82,15 @@ func SignedInUser(ctx *macaron.Context, sess session.Store) (*models.User, bool)
 		return nil, false
 	}
 
-	uid := SignedInID(ctx, sess)
+	if uid := SignedInID(ctx, sess); uid > 0 {
+		user, err := models.GetUserByID(uid)
+		if err == nil {
+			return user, false
+		} else if !models.IsErrUserNotExist(err) {
+			log.Error(4, "GetUserById: %v", err)
+		}
+	}
 
-	if uid <= 0 {
 	if setting.Service.EnableReverseProxyAuth {
 		webAuthUser := ctx.Req.Header.Get(setting.ReverseProxyAuthUser)
 		if len(webAuthUser) > 0 {
@@ -143,14 +142,6 @@ func SignedInUser(ctx *macaron.Context, sess session.Store) (*models.User, bool)
 	return nil, false
 }
 
-	u, err := models.GetUserByID(uid)
-	if err != nil {
-		log.Error(4, "GetUserById: %v", err)
-		return nil, false
-	}
-	return u, false
-}
-
 // Form form binding interface
 type Form interface {
 	binding.Validator