submodule update: run at most one fetch job unless otherwise set
In
a028a1930c (fetching submodules: respect `submodule.fetchJobs`
config option, 2016-02-29), we made sure to keep the default
behavior of fetching at most one submodule at once when not setting
the newly introduced `submodule.fetchJobs` config.
This regressed in
90efe595c5 (builtin/submodule--helper: factor
out submodule updating, 2018-08-03). Fix it.
Reported-by: Sjon Hortensius <sjon@parse.nl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>