Fix Span LastIndexOf empty value handling

diff --git a/src/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs b/src/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs
index a53ed19..58d0b5c 100644 (file)
--- a/src/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs
+++ b/src/System.Private.CoreLib/shared/System/MemoryExtensions.Fast.cs
@@ -188,7 +188,7 @@ namespace System
 
             if (value.Length == 0)
             {
-                return 0;
+                return span.Length - 1;
             }
 
             if (span.Length == 0)