sync: halt file discovery if repo has no servers

This avoids error spam when no servers are configured for a repo and a
sync operation is performed:

Proceed with installation? [Y/n] y
:: Retrieving packages from testing...
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing
warning: failed to retrieve some files from testing

Signed-off-by: Dave Reisner <dreisner@archlinux.org>
Signed-off-by: Dan McGee <dan@archlinux.org>

0 files changed, 0 insertions, 0 deletions