fix behavior for new issue

src/libraries/Microsoft.Extensions.Primitives/src/StringSegment.cs

@@ -520,12 +520,12 @@ public int IndexOfAny(char[] anyOf, int startIndex, int count)
 
             if (HasValue)
             {
-                if (startIndex < 0 || Offset + startIndex > Buffer.Length)
+                if (startIndex < 0 || startIndex > Length)
                 {
                     ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
                 }
 
-                if (count < 0 || Offset + startIndex + count > Buffer.Length)
+                if (count < 0 || startIndex + count > Length)
                 {
                     ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count);
                 }