ChatControlBase: Fix scroll hotkey infinite recursion

Handling of SHIFT + PAGE_UP/PAGE_DOWN was missing in the
ConversationTextview key press handler
3 jobs for master in 5 minutes and 8 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #20170
run-appdata

00:00:12

passed #20169
run-tests

00:04:40

 
  Build
passed #20171
run-build

00:00:15