ntdll: check for string and stringlength in _wcslwr and _wcsupr

[André Hentschel]

Fixes http://bugs.winehq.org/show_bug.cgi?id=28303 (str="")
---
 dlls/ntdll/wcstring.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/dlls/ntdll/wcstring.c b/dlls/ntdll/wcstring.c
index 7f0035d..d75f10e 100644
--- a/dlls/ntdll/wcstring.c
+++ b/dlls/ntdll/wcstring.c
@@ -47,6 +47,7 @@ INT __cdecl NTDLL__wcsicmp( LPCWSTR str1, LPCWSTR str2 )
  */
 LPWSTR __cdecl NTDLL__wcslwr( LPWSTR str )
 {
+    if (!str || !*str) return NULL;
     return strlwrW( str );
 }
 
@@ -65,6 +66,7 @@ INT __cdecl NTDLL__wcsnicmp( LPCWSTR str1, LPCWSTR str2, INT n )
  */
 LPWSTR __cdecl NTDLL__wcsupr( LPWSTR str )
 {
+    if (!str || !*str) return NULL;
     return struprW( str );
 }
 
-- 

Best Regards, André Hentschel