update download error hint

app/app-detail.component.ts

@@ -164,7 +164,15 @@ export class AppDetailComponent implements OnInit, OnChanges {
             }
         } catch (e) {
             console.error(e);
-            new Notification(targetApp.name, {body: '下载失败 ' + e.message});
+            let errmsg = e.message || e.toString();
+            if (errmsg.includes('No URI available')) {
+                errmsg = '所有的备用下载地址都无法连接';
+            }
+            let errmsgMatch = errmsg.match(/message: (.+)/);
+            if (errmsgMatch) {
+                errmsg = errmsgMatch[1];
+            }
+            new Notification(targetApp.name, { body: '下载失败: ' + errmsg });
         }
     }