mshtml: Don't try to null terminate post data if it's not available.

dlls/mshtml/navigate.c

@@ -902,6 +902,7 @@ static HRESULT read_post_data_stream(nsIInputStream *stream, BOOL contains_heade
         post_data = new_data;
     }
 
+    if(post_data)
         post_data[data_len] = 0;
     request_data->post_data = post_data;
     request_data->post_data_len = data_len;