Fix BitScanForward() usage

Should fix Win64 bot.

src/hb-private.hh

diff --git a/src/hb-private.hh b/src/hb-private.hh
index 583b561..daa496e 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -458,14 +458,14 @@
   {
     unsigned long where;
     _BitScanForward (&where, v);
-    return 1 + where;
+    return where;
   }
 # if _WIN64
   if (sizeof (T) <= 8)
   {
     unsigned long where;
     _BitScanForward64 (&where, v);
-    return 1 + where;
+    return where;
   }
 # endif
 #endif