Perform check and safe checks first

This moves the issue presence check to the first place (as it should be)
and doesn't check for feature availability until we know we need to.

app/services/issues/base_service.rb

@@ -22,12 +22,13 @@ module Issues
     NO_REBALANCING_NEEDED = ((RelativePositioning::MIN_POSITION * 0.9999)..(RelativePositioning::MAX_POSITION * 0.9999)).freeze
 
     def rebalance_if_needed(issue)
-      gates = [issue.project, issue.project.group].compact
-      return unless gates.any? { |gate| Feature.enabled?(:rebalance_issues, gate) }
       return unless issue
       return if issue.relative_position.nil?
       return if NO_REBALANCING_NEEDED.cover?(issue.relative_position)
 
+      gates = [issue.project, issue.project.group].compact
+      return unless gates.any? { |gate| Feature.enabled?(:rebalance_issues, gate) }
+
       IssueRebalancingWorker.perform_async(issue.id)
     end