Fix caching for zsh completions
Fix caching for zsh completions

Before - failing to find completions in the relevant variable would always
force getting them fresh, regardless of whether they are present in the cache
because the `||` would always be true.

- in _bazel_get_options use a short circuit return when the variable is not
  empty
- in _bazel_command, _bazel_help_topic, and _bazel_info_key nest the cache
  conditions inside the if block checking for an empty varible

cleanup:
- Use the same 2 space indent for continued conditions in _bazel_get_options as
  was already used in _bazel_command and the rest

Closes #1951.

--
Reviewed-on: https://github.com/bazelbuild/bazel/pull/1951
MOS_MIGRATED_REVID=136458728

zhexuany/bazel,dslomov/bazel,kchodorow/bazel-1,hermione521/bazel,spxtr/bazel,aehlig/bazel,dropbox/bazel,snnn/bazel,damienmg/bazel,mikelikespie/bazel,LuminateWireless/bazel,dropbox/bazel,dslomov/bazel,bazelbuild/bazel,kchodorow/bazel-1,dslomov/bazel,aehlig/bazel,Asana/bazel,dropbox/bazel,dslomov/bazel,kchodorow/bazel,snnn/bazel,perezd/bazel,mbrukman/bazel,akira-baruah/bazel,LuminateWireless/bazel,katre/bazel,davidzchen/bazel,zhexuany/bazel,juhalindfors/bazel-patches,juhalindfors/bazel-patches,mbrukman/bazel,cushon/bazel,hermione521/bazel,kchodorow/bazel,perezd/bazel,kchodorow/bazel,Asana/bazel,meteorcloudy/bazel,davidzchen/bazel,werkt/bazel,katre/bazel,ulfjack/bazel,perezd/bazel,hermione521/bazel,ulfjack/bazel,mikelikespie/bazel,mbrukman/bazel,cushon/bazel,LuminateWireless/bazel,hermione521/bazel,katre/bazel,damienmg/bazel,juhalindfors/bazel-patches,katre/bazel,safarmer/bazel,cushon/bazel,mikelikespie/bazel,spxtr/bazel,twitter-forks/bazel,aehlig/bazel,werkt/bazel,kchodorow/bazel-1,davidzchen/bazel,safarmer/bazel,twitter-forks/bazel,damienmg/bazel,akira-baruah/bazel,mikelikespie/bazel,meteorcloudy/bazel,werkt/bazel,bazelbuild/bazel,safarmer/bazel,meteorcloudy/bazel,ButterflyNetwork/bazel,dslomov/bazel-windows,snnn/bazel,ButterflyNetwork/bazel,dslomov/bazel-windows,perezd/bazel,cushon/bazel,twitter-forks/bazel,LuminateWireless/bazel,akira-baruah/bazel,dslomov/bazel-windows,zhexuany/bazel,ulfjack/bazel,dropbox/bazel,ButterflyNetwork/bazel,dslomov/bazel,katre/bazel,twitter-forks/bazel,snnn/bazel,mbrukman/bazel,safarmer/bazel,Asana/bazel,variac/bazel,akira-baruah/bazel,spxtr/bazel,ulfjack/bazel,davidzchen/bazel,hermione521/bazel,ulfjack/bazel,ButterflyNetwork/bazel,cushon/bazel,bazelbuild/bazel,aehlig/bazel,kchodorow/bazel-1,ButterflyNetwork/bazel,variac/bazel,dslomov/bazel-windows,damienmg/bazel,dslomov/bazel,akira-baruah/bazel,Asana/bazel,werkt/bazel,twitter-forks/bazel,davidzchen/bazel,perezd/bazel,zhexuany/bazel,dropbox/bazel,juhalindfors/bazel-patches,kchodorow/bazel,juhalindfors/bazel-patches,spxtr/bazel,variac/bazel,damienmg/bazel,aehlig/bazel,aehlig/bazel,mbrukman/bazel,ulfjack/bazel,damienmg/bazel,variac/bazel,davidzchen/bazel,mikelikespie/bazel,werkt/bazel,dslomov/bazel,safarmer/bazel,spxtr/bazel,Asana/bazel,perezd/bazel,mbrukman/bazel,mikelikespie/bazel,snnn/bazel,aehlig/bazel,juhalindfors/bazel-patches,hermione521/bazel,kchodorow/bazel,ButterflyNetwork/bazel,variac/bazel,variac/bazel,akira-baruah/bazel,cushon/bazel,werkt/bazel,snnn/bazel,LuminateWireless/bazel,bazelbuild/bazel,snnn/bazel,twitter-forks/bazel,kchodorow/bazel-1,spxtr/bazel,zhexuany/bazel,bazelbuild/bazel,kchodorow/bazel-1,juhalindfors/bazel-patches,kchodorow/bazel,zhexuany/bazel,meteorcloudy/bazel,perezd/bazel,bazelbuild/bazel,variac/bazel,spxtr/bazel,twitter-forks/bazel,meteorcloudy/bazel,davidzchen/bazel,LuminateWireless/bazel,dslomov/bazel-windows,meteorcloudy/bazel,Asana/bazel,damienmg/bazel,dslomov/bazel-windows,dropbox/bazel,meteorcloudy/bazel,ulfjack/bazel,Asana/bazel,safarmer/bazel,kchodorow/bazel,katre/bazel