fetch: do not run a redundant fetch from submodule

When 7dce19d3 (fetch/pull: Add the --recurse-submodules option, 2010-11-12) introduced the "--recurse-submodule" option, the approach taken was to perform fetches in submodules only once, after all the main fetching (it may usually be a fetch from a single remote, but it could be fetching from a group of remotes using fetch_multiple()) succeeded. Later we added "--all" to fetch from all defined remotes, which complicated things even more. If your project has a submodule, and you try to run "git fetch --recurse-submodule --all", you'd see a fetch for the top-level, which invokes another fetch for the submodule, followed by another fetch for the same submodule. All but the last fetch for the submodule come from a "git fetch --recurse-submodules" subprocess that is spawned via the fetch_multiple() interface for the remotes, and the last fetch comes from the code at the end. Because recursive fetching from submodules is done in each fetch for the top-level in fetch_multiple(), the last fetch in the submodule is redundant. It only matters when fetch_one() interacts with a single remote at the top-level. While we are at it, there is one optimization that exists in dealing with a group of remote, but is missing when "--all" is used. In the former, when the group turns out to be a group of one, instead of spawning "git fetch" as a subprocess via the fetch_multiple() interface, we use the normal fetch_one() code path. Do the same when handing "--all", if it turns out that we have only one remote defined. Reviewed-by: Glen Choo <chooglen@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>