Add missing handle validation to templates

system/service/template.go

@@ -191,6 +191,10 @@ func (svc template) Create(ctx context.Context, new *types.Template) (tpl *types
 	)
 
 	err = func() (err error) {
+		if !handle.IsValid(new.Handle) {
+			return TemplateErrInvalidHandle()
+		}
+
 		if !svc.ac.CanCreateTemplate(ctx) {
 			return TemplateErrNotAllowedToCreate()
 		}
@@ -227,6 +231,10 @@ func (svc template) Update(ctx context.Context, upd *types.Template) (tpl *types
 			return TemplateErrInvalidID()
 		}
 
+		if !handle.IsValid(upd.Handle) {
+			return TemplateErrInvalidHandle()
+		}
+
 		if tpl, err = store.LookupTemplateByID(ctx, svc.store, upd.ID); err != nil {
 			return
 		}