http.c: A->W bugfix

[Aric Stewart]

when converting SendRequestExA -> W we need to set the lpcszHeader 
parameter to NULL if the original one is NULL.
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Index: dlls/wininet/http.c
===================================================================
RCS file: /home/wine/wine/dlls/wininet/http.c,v
retrieving revision 1.132
diff -u -r1.132 http.c
--- dlls/wininet/http.c	3 Dec 2005 18:35:15 -0000	1.132
+++ dlls/wininet/http.c	7 Dec 2005 17:01:23 -0000
@@ -1532,6 +1541,8 @@
                     lpBuffersIn->lpcszHeader, lpBuffersIn->dwHeadersLength,
                     (LPWSTR)BuffersInW.lpcszHeader, headerlen);
         }
+        else
+            BuffersInW.lpcszHeader = NULL;
         BuffersInW.dwHeadersTotal = lpBuffersIn->dwHeadersTotal;
         BuffersInW.lpvBuffer = lpBuffersIn->lpvBuffer;
         BuffersInW.dwBufferLength = lpBuffersIn->dwBufferLength;