Fix selecting multiple entities and training.
Fixes a visual bug where selecting a trainer and a non-trainer counted as two.
Introduced in r26000 / rP26000
Reported by Purgator_ on the forums: https://wildfiregames.com/forum/topic/67583-r26182-ui-logic-bug.
Differential revision: https://code.wildfiregames.com/D4432
Tested by: @Langbart
Fixes: #6415