wininet: Use HTTP_ADDHDR_FLAG_REPLACE flag in HTTP_HttpSendRequest to add Content-Length header.

dlls/wininet/http.c

@@ -2240,7 +2240,8 @@ BOOL WINAPI HTTP_HttpSendRequestW(LPWININETHTTPREQW lpwhr, LPCWSTR lpszHeaders,
             'C','o','n','t','e','n','t','-','L','e','n','g','t','h',':',' ','%','l','i','\r','\n',0};
         WCHAR contentLengthStr[sizeof szContentLength/2 /* includes \n\r */ + 20 /* int */ ];
         sprintfW(contentLengthStr, szContentLength, dwContentLength);
-        HTTP_HttpAddRequestHeadersW(lpwhr, contentLengthStr, -1L, HTTP_ADDREQ_FLAG_ADD);
+        HTTP_HttpAddRequestHeadersW(lpwhr, contentLengthStr, -1L,
+                HTTP_ADDREQ_FLAG_ADD | HTTP_ADDHDR_FLAG_REPLACE);
     }
 
     Host = HTTP_GetHeader(lpwhr,szHost);