fix for GetPrinterDriverDirectoryA

[Stefan Leichter <Stefan.Leichter@camLine.com>]

ChangeLog
-------------
	GetPrinterDriverDirectoryA: do not crash on Null pointers

--- ../wine/dlls/winspool/info.c	Fri Jan  3 11:57:13 2003
+++ dlls/winspool/info.c	Tue Jan  7 10:33:43 2003
@@ -2503,10 +2503,11 @@
     if (ret) {
         ret = WideCharToMultiByte( CP_ACP, 0, driverDirectoryW, -1, 
                                    pDriverDirectory, cbBuf, NULL, NULL);
+        if(pcbNeeded)
         *pcbNeeded = WideCharToMultiByte( CP_ACP, 0, driverDirectoryW, -1,
                                    NULL, 0, NULL, NULL);
     } else 
-        *pcbNeeded = pcbNeededW * sizeof(CHAR)/sizeof(WCHAR);
+        if(pcbNeeded) *pcbNeeded = pcbNeededW * sizeof(CHAR)/sizeof(WCHAR);
 
     TRACE("provided<%ld> required <%ld>\n", cbBuf, *pcbNeeded);