enhance: only show two chars when they are all ascii letters or digits (#585)

Author: love-linger

src/Views/Avatar.cs

@@ -128,10 +128,9 @@ private static string GetFallbackString(string name)
             foreach (var part in parts)
                 chars.Add(part[0]);
 
-            if (chars.Count >= 2)
+            if (chars.Count >= 2 && char.IsAsciiLetterOrDigit(chars[0]) && char.IsAsciiLetterOrDigit(chars[^1]))
                 return string.Format("{0}{1}", chars[0], chars[^1]);
-            if (chars.Count == 1)
-                return string.Format("{0}", chars[0]);
+                
             return name.Substring(0, 1);
         }