fix(list): when list background is removed, delete file from file system and DB (#1372)

Co-authored-by: testinho.testador <testinho.testador@noreply.kolaente.de>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/1372
Reviewed-by: konrad <k@knt.li>
Co-authored-by: clos <clos@noreply.kolaente.de>
Co-committed-by: clos <clos@noreply.kolaente.de>

pkg/modules/background/handler/background.go

@@ -341,6 +341,11 @@ func RemoveListBackground(c echo.Context) error {
 		return err
 	}
 
+	err = list.DeleteBackgroundFileIfExists()
+	if err != nil {
+		return err
+	}
+
 	list.BackgroundFileID = 0
 	list.BackgroundInformation = nil
 	list.BackgroundBlurHash = ""