a11y/entry: Fix copy-pasteo re 2ndary icon tooltip

The else case was wrongly resetting the accessible description on the
primary icon, which might not exist and can therefore cause a crash.

#1160
4 jobs for 1160-crash-clearing-gtkentry-icon-tooltip-master in 23 minutes and 55 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed fedora-x86_64 #50162

00:07:40

passed msys2-mingw32 #50163
win32

00:04:18

 
  Flatpak
passed flatpak:demo #50164

00:16:14

passed flatpak:widget-factory #50165

00:08:01