screensaver: queue key events while unlock dialog is not ready

Unlock dialog is created in idle after keyboard and/or mouse
activity and its visibility/readiness depends on PAM.

This means that first key event will never reach unlock dialog if
it was not already created/ready. If user is fast enough more key
events might not reach dialog.

Queue key events in this case and forward to password entry when
dialog becomes visible.

#49
3 jobs for master in 13 minutes and 9 seconds
Status Job ID Name Coverage
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passed #683433
menu

00:00:34

 
  Build
passed #683434
ubuntu

00:12:34

 
  Analysis
manual #683435
allowed to fail manual
coverity