Refactored jira issue enforcement method

ee/app/models/ee/project.rb

@@ -771,9 +771,7 @@ module EE
     end
 
     def prevent_merge_without_jira_issue?
-      return false unless jira_issue_association_required_to_merge_enabled?
-
-      prevent_merge_without_jira_issue
+      jira_issue_association_required_to_merge_enabled? && prevent_merge_without_jira_issue
     end
 
     private