ntdll: Use default casemap and codepage file names if the value in registry is empty.

This helps to keep compatibility with old prefixes being reused for wine-5.0.
Old prefixes in their registry have

[System\\CurrentControlSet\\Control\\Nls\\Codepage]
"37"=""

[System\\CurrentControlSet\\Control\\Nls\\Language]
"0409"=""

and this leads to LCMapString(LCMAP_LOWERCASE/LCMAP_UPPERCASE) return garbage.

This is a regression caused by 94a3add0ea.

Signed-off-by: Dmitry Timoshkov <dmitry@baikal.ru>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/ntdll/locale.c

@@ -218,7 +218,7 @@ static NTSTATUS open_nls_data_file( ULONG type, ULONG id, HANDLE *file )
         NtClose( handle );
     }
 
-    if (!name)  /* otherwise some hardcoded defaults */
+    if (!name || !*name)  /* otherwise some hardcoded defaults */
     {
         switch (type)
         {