Added handling for empty extension parameters in ImageFormatManager.TryFindFormatByFileExtension

src/ImageSharp/Formats/ImageFormatManager.cs

@@ -102,9 +102,12 @@ public class ImageFormatManager
     /// <returns><see langword="true"/> if a match is found; otherwise, <see langword="false"/></returns>
     public bool TryFindFormatByFileExtension(string extension, [NotNullWhen(true)] out IImageFormat? format)
     {
-        if (extension[0] == '.')
+        if (!string.IsNullOrWhiteSpace(extension))
         {
-            extension = extension[1..];
+            if (extension[0] == '.')
+            {
+                extension = extension[1..];
+            }
         }
 
         format = this.imageFormats.FirstOrDefault(x =>