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
1 job for 1160-crash-clearing-gtkentry-icon-tooltip in 8 minutes and 38 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build #50166

00:08:38