Allow updating draft releases while keeping them as draft

Closes #162

routers/repo/release.go

@@ -247,6 +247,7 @@ func EditRelease(ctx *context.Context) {
 	ctx.Data["title"] = rel.Title
 	ctx.Data["content"] = rel.Note
 	ctx.Data["prerelease"] = rel.IsPrerelease
+	ctx.Data["IsDraft"] = rel.IsDraft
 
 	ctx.HTML(200, RELEASE_NEW)
 }