URLMON: fix call to ReadFile

[Thomas Weidenmueller]

The last two parameters passed to ReadFile may never be NULL.
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Index: dlls/urlmon/umstream.c
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RCS file: /home/wine/wine/dlls/urlmon/umstream.c,v
retrieving revision 1.2
diff -u -r1.2 umstream.c
--- dlls/urlmon/umstream.c	3 Jul 2005 12:05:03 -0000	1.2
+++ dlls/urlmon/umstream.c	8 Dec 2005 19:19:02 -0000
@@ -225,6 +225,7 @@
                                       ULONG cb,
                                       ULONG* pcbRead)
 {
+    DWORD dwBytesRead;
     IUMCacheStream *This = (IUMCacheStream *)iface;
 
     TRACE("(%p)->(%p,0x%08lx,%p)\n",This, pv, cb, pcbRead);
@@ -232,7 +233,7 @@
     if ( !pv )
        return STG_E_INVALIDPOINTER;
 
-    if ( ! ReadFile( This->handle, pv, cb, pcbRead, NULL ) )
+    if ( ! ReadFile( This->handle, pv, cb, (pcbRead ? pcbRead : &dwBytesRead), NULL ) )
        return S_FALSE;
 
     if (!*pcbRead)