fix shuffle mode in the slideshow

1 job for master in 60 minutes and 1 second (queued for 19 minutes and 48 seconds)
Status Job ID Name Coverage
  Build
failed #56180
linux kf5-qt5 qt5.12

01:00:01

 
Name Stage Failure
failed
linux kf5-qt5 qt5.12 Build The script exceeded the maximum execution time set for the job
[ 77%] Building CXX object core/dplugins/generic/webservices/pinterest/CMakeFiles/Generic_Pinterest_Plugin.dir/ptalker.cpp.o
[ 77%] Building CXX object core/dplugins/generic/webservices/onedrive/CMakeFiles/Generic_OneDrive_Plugin.dir/odplugin.cpp.o
[ 77%] Building CXX object core/dplugins/generic/webservices/rajce/CMakeFiles/Generic_Rajce_Plugin.dir/rajcewindow.cpp.o
[ 77%] Building CXX object core/dplugins/generic/webservices/smugmug/CMakeFiles/Generic_SmugMug_Plugin.dir/smugwidget.cpp.o
[ 77%] Building CXX object core/dplugins/generic/webservices/onedrive/CMakeFiles/Generic_OneDrive_Plugin.dir/odtalker.cpp.o
[ 77%] Building CXX object core/dplugins/generic/webservices/piwigo/CMakeFiles/Generic_Piwigo_Plugin.dir/piwigowindow.cpp.o
Uploading artifacts for failed job
Pulling docker image gitlab/gitlab-runner-helper:x86_64-6fbc7474 ...
ERROR: Job failed: execution took longer than 1h0m0s seconds