shlwapi: Use the appropriate constant for an uninitialized TLS check.

dlls/shlwapi/thread.c

diff --git a/dlls/shlwapi/thread.c b/dlls/shlwapi/thread.c
index 58888f7..3be58cc 100644
--- a/dlls/shlwapi/thread.c
+++ b/dlls/shlwapi/thread.c
@@ -180,7 +180,7 @@
 {
   TRACE("(%p)\n", lpUnknown);
 
-  if (!lpUnknown || SHLWAPI_ThreadRef_index  == 0xffffffff)
+  if (!lpUnknown || SHLWAPI_ThreadRef_index  == TLS_OUT_OF_INDEXES)
     return E_NOINTERFACE;
 
   TlsSetValue(SHLWAPI_ThreadRef_index, lpUnknown);