Make google-ima a valid injectable scriptlet

Related feedback:
https://www.reddit.com/r/uBlockOrigin/comments/1m4dbk1/ublock_being_detected_on_south_park_studios/

src/js/redirect-engine.js

@@ -210,6 +210,7 @@ class RedirectEngine {
         const entry = this.resources.get(this.aliases.get(name) || name);
         if ( entry === undefined ) { return; }
         if ( entry.mime.startsWith(mime) === false ) { return; }
+        if ( entry.data === undefined ) { return; }
         return {
             js: entry.toContent(),
             world: entry.world,

src/js/redirect-resources.js

@@ -94,6 +94,7 @@ export default new Map([
     } ],
     [ 'google-ima.js', {
         alias: 'google-ima3',                       /* adguard compatibility */
+        data: 'text',
     } ],
     [ 'googlesyndication_adsbygoogle.js', {
         alias: [