Update Block a user form (#37359)

Use the new "form-fetch-action" for better user experience, and use
JSONError to show error messages.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/v1/shared/block.go

@@ -9,6 +9,7 @@ import (
 
 	user_model "code.gitea.io/gitea/models/user"
 	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/routers/api/v1/utils"
 	"code.gitea.io/gitea/services/context"
 	"code.gitea.io/gitea/services/convert"
@@ -48,17 +49,14 @@ func CheckUserBlock(ctx *context.APIContext, blocker *user_model.User) {
 		return
 	}
 
-	status := http.StatusNotFound
-	blocking, err := user_model.GetBlocking(ctx, blocker.ID, blockee.ID)
-	if err != nil {
+	_, err = user_model.GetBlocking(ctx, blocker.ID, blockee.ID)
+	if errors.Is(err, util.ErrNotExist) {
+		ctx.Status(http.StatusNotFound)
+	} else if err == nil {
+		ctx.Status(http.StatusNoContent)
+	} else {
 		ctx.APIErrorInternal(err)
-		return
 	}
-	if blocking != nil {
-		status = http.StatusNoContent
-	}
-
-	ctx.Status(status)
 }
 
 func BlockUser(ctx *context.APIContext, blocker *user_model.User) {