Fix: File not found when the solution is opened

Author: loop8ack

src/ExtensionManager/Features/Install/InstallFeatureBase.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -52,6 +53,9 @@ public async Task ExecuteAsync()
         if (filePath is null or { Length: 0 })
             return;
 
+        if (!File.Exists(filePath))
+            return;
+
         var installedExtensions = await Extensions.GetInstalledExtensionsAsync().ConfigureAwait(false);
         var manifest = await ManifestService.ReadAsync(filePath).ConfigureAwait(false);