Attempt to fix Windows bug

source/adios2/toolkit/transport/file/FileFStream.cpp

@@ -145,8 +145,8 @@ size_t FileFStream::GetSize()
 {
     const auto currentPosition = m_FileStream.tellg();
     m_FileStream.seekg(0, std::ios_base::end);
-    const auto size = m_FileStream.tellg();
-    if (size == -1)
+    const std::streampos size = m_FileStream.tellg();
+    if (static_cast<int>(size) == -1)
     {
         throw std::ios_base::failure("ERROR: couldn't get size of " + m_Name +
                                      " file\n");