gclient: print an error message instead of crashing
gclient: print an error message instead of crashing

When 'gclient recurse' is called from a unconfigured directory.
No functional change otherwise.

R=bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org
Bug:774749
Change-Id: Ifb2b74c042ce31faf3e1287c5614739e58e9178c
Reviewed-on: https://chromium-review.googlesource.com/726419
Reviewed-by: Aaron Gable <bbed39beedae4cdb499af742d2fcd6c63934d93b@chromium.org>
Commit-Queue: Marc-Antoine Ruel <d2bf0fc09b08f7b0888b3ddab32b3e89c7122c8b@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools