nsis: Read installed components from 64-bit registry

* src/nsis/installer.nsi: Switch back to 64-bit registry before calling
MementoSectionRestore.

The installed components are written to the 64-bit registry (unless
browser integration was installed; see T8038), but they were read from
the 32-bit registry. With this change they are written to and read from
the 64-bit registry.

• GnuPG-bug-id: T8039