show error message for missing theme

desirae.js

@@ -267,6 +267,10 @@
     if (!themename) {
       themename = desi.site.theme || desi.config.theme;
     }
+    if (!desi.config.themes[themename]) {
+      console.error("'" + themename + "' was not found among the themes");
+      return arr;
+    }
 
     // TODO NO DEFAULTS
     if ('__page__' === layoutname) {