Fix daemon memory killer busy loop risk

StandardError will cause busy loop in start_working. Simple fix is
to always `sleep` first in each loop iteration

lib/gitlab/sidekiq_daemon/memory_killer.rb

@@ -39,8 +39,8 @@ module Gitlab
 
         while enabled?
           begin
-            restart_sidekiq unless rss_within_range?
             sleep(CHECK_INTERVAL_SECONDS)
+            restart_sidekiq unless rss_within_range?
           rescue => e
             log_exception(e, __method__)
           rescue Exception => e # rubocop:disable Lint/RescueException

spec/lib/gitlab/sidekiq_daemon/memory_killer_spec.rb

@@ -40,6 +40,7 @@ describe Gitlab::SidekiqDaemon::MemoryKiller do
             message: "Exception from start_working: My Exception")
 
         expect(memory_killer).to receive(:rss_within_range?).twice.and_raise(StandardError, 'My Exception')
+        expect(memory_killer).to receive(:sleep).twice.with(Gitlab::SidekiqDaemon::MemoryKiller::CHECK_INTERVAL_SECONDS)
 
         expect { subject }.not_to raise_exception
       end
@@ -53,6 +54,7 @@ describe Gitlab::SidekiqDaemon::MemoryKiller do
 
         expect(memory_killer).to receive(:rss_within_range?).once.and_raise(Exception, 'My Exception')
 
+        expect(memory_killer).to receive(:sleep).with(Gitlab::SidekiqDaemon::MemoryKiller::CHECK_INTERVAL_SECONDS)
         expect(Sidekiq.logger).to receive(:warn).once
           .with(
             class: described_class.to_s,