gluon-site: always provide a PKG_VERSION, also during package scan

package/gluon-site/Makefile

 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=gluon-site
-PKG_VERSION:=$(GLUON_SITE_CODE)
-PKG_RELEASE:=0.$(GLUON_RELEASE)
+PKG_VERSION:=$(if $(GLUON_SITE_CODE),$(GLUON_SITE_CODE),1)
+PKG_RELEASE:=$(GLUON_RELEASE)
 
 PKG_FILE_DEPENDS := $(GLUON_SITEDIR)/
 PKG_BUILD_DEPENDS := luci