Improve condition for use of pubsetbuf

Using this function like this seems only be possible with `libstdc++`. The
standard lib of MSVC does not support it as well. So use it only with
`libstdc++`.

io/passwordfile.cpp

@@ -349,10 +349,10 @@ void PasswordFile::load()
     stringstream decryptedStream(stringstream::in | stringstream::out | stringstream::binary);
     decryptedStream.exceptions(ios_base::failbit | ios_base::badbit);
     try {
-#ifdef _LIBCPP_VERSION
-        decryptedStream.write(decryptedData.data(), static_cast<streamsize>(remainingSize));
-#else
+#if defined(__GLIBCXX__) && !defined(_LIBCPP_VERSION)
         decryptedStream.rdbuf()->pubsetbuf(decryptedData.data(), static_cast<streamsize>(remainingSize));
+#else
+        decryptedStream.write(decryptedData.data(), static_cast<streamsize>(remainingSize));
 #endif
         if (m_version >= 0x5u) {
             BinaryReader reader(&decryptedStream);