U4-7823 - stop flooding the log with errors getting media 0

src/Umbraco.Web/PublishedCache/XmlPublishedCache/PublishedMediaCache.cs

@@ -182,6 +182,8 @@ namespace Umbraco.Web.PublishedCache.XmlPublishedCache
             // it is called, but at least it should NOT hit the database
             // nor Lucene each time, relying on the memory cache instead
 
+	        if (id <= 0) return null; // fail fast
+
 	        var cacheValues = GetCacheValues(id, GetUmbracoMediaCacheValues);
 
 	        return cacheValues == null ? null : CreateFromCacheValues(cacheValues);