Properly report network error condition when importing filter list

Before this commit, a network error condition was not reported
when the filter list was imported, it was only reported afterward
when the imported filter list was updated.

Author: gorhill

src/js/assets.js

@@ -787,13 +787,17 @@ assets.get = async function(assetKey, options = {}) {
         contentURLs.push(...assetDetails.cdnURLs);
     }
 
+    let error = 'ENOTFOUND';
     for ( const contentURL of contentURLs ) {
         if ( reIsExternalPath.test(contentURL) && assetDetails.hasLocalURL ) {
             continue;
         }
         const details = assetDetails.content === 'filters'
             ? await assets.fetchFilterList(contentURL)
             : await assets.fetchText(contentURL);
+        if ( details.error !== undefined ) {
+            error = details.error;
+        }
         if ( details.content === '' ) { continue; }
         if ( reIsExternalPath.test(contentURL) && options.dontCache !== true ) {
             assetCacheWrite(assetKey, {
@@ -804,7 +808,12 @@ assets.get = async function(assetKey, options = {}) {
         }
         return reportBack(details.content, contentURL);
     }
-    return reportBack('', '', 'ENOTFOUND');
+    if ( assetRegistry[assetKey] !== undefined ) {
+        registerAssetSource(assetKey, {
+            error: { time: Date.now(), error }
+        });
+    }
+    return reportBack('', '', error);
 };
 
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