🐛 Fix logic bug regarding splitting job

Co-authored-by: Kirk Wang <kirk.wang@scientist.com>

lib/iiif_print/jobs/request_split_pdf_job.rb

@@ -8,7 +8,7 @@ class RequestSplitPdfJob < IiifPrint::Jobs::ApplicationJob
       # @param user [User]
       # rubocop:disable Metrics/MethodLength
       def perform(file_set:, user:)
-        return true if file_set.pdf?
+        return true unless file_set.pdf?
 
         work = IiifPrint.parent_for(file_set)