test_keyval_visit_size() should test for trailing crap after size with
and without suffix.  It does test the latter: "sz2=16Gi" has size
"16G" followed by crap "i".  It fails to test the former "sz1=16E" is
a syntactically valid size that overflows uint64_t.  Replace by
"sz1=0Z".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20191125133846.27790-3-armbru@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>