...found with GCC 9, where the standard library iterator implementations are
apparently sufficiently different to older versions of GCC to find more cases
of !(... == ...) vs. ... != ...

Change-Id: Ibe7c5140049a69d2c5318b4b2371f2e66bd05028
Reviewed-on: https://gerrit.libreoffice.org/68012
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>