Address AI feedback

Signed-off-by: Lukasz Gryglicki <[email protected]>

Assisted by [OpenAI](https://platform.openai.com/)

Assisted by [GitHub Copilot](https://github.com/features/copilot)

Author: lukaszgryglicki

cla-backend-go/v2/signatures/zip_builder.go

@@ -153,6 +153,9 @@ func (z *Zipper) buildPDFZip(claType string, claGroupID string) error {
 	}()
 	zipUpdated = writeFileToZip(writer, downloaderOutputChan)
 	if listErr := <-listErrCh; listErr != nil {
+		if cerr := writer.Close(); cerr != nil {
+			log.Warnf("zip writer close failed: %v", cerr)
+		}
 		return listErr
 	}
 	if cerr := writer.Close(); cerr != nil {