(The unnecessary os.setstate(std::ios_base::failbit) was due to a misreading of
C++17 [ostream.formatted.reqmts]/1.)

Change-Id: I7d8285230cb316c7af45c76029e9629517d05d56
Reviewed-on: https://gerrit.libreoffice.org/65217
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>