Use Uri class to combine store location with thumb path in GetThumbUrl

Agent-Logs-Url: https://github.com/grandnode/grandnode2/sessions/19f059e0-4b1b-4db9-b30b-56e92247bc80

Co-authored-by: KrzysztofPajak <16772986+KrzysztofPajak@users.noreply.github.com>

Author: Copilot

src/Business/Grand.Business.Storage/Services/PictureService.cs

@@ -158,8 +158,11 @@ protected virtual async Task<string> GetThumbPhysicalPath(string thumbFileName)
     /// <returns>Local picture thumb path</returns>
     protected virtual string GetThumbUrl(string thumbFileName, string storeLocation = null)
     {
-        storeLocation = !string.IsNullOrEmpty(storeLocation) ? storeLocation : string.Empty;
-        return storeLocation.TrimEnd('/') + _mediaFileStore.Combine(ImageThumbPath, thumbFileName);
+        var thumbPath = _mediaFileStore.Combine(ImageThumbPath, thumbFileName);
+        if (string.IsNullOrEmpty(storeLocation))
+            return thumbPath;
+
+        return new Uri(new Uri(storeLocation), thumbPath).ToString();
     }
 
     /// <summary>