fix race condition that caused duplicate palette button indicators to be created
fix race condition that caused duplicate palette button indicators to be created

pikurasa/musicblocks,Kachachan/musicblocks,hemantkasat/musicblocks,tradzik/musicblocks,Kachachan/musicblocks,hemantkasat/musicblocks,pikurasa/musicblocks,hemantkasat/musicblocks,sneh1234/musicblocks,tradzik/musicblocks,sneh1234/musicblocks,tradzik/musicblocks,sneh1234/musicblocks,Kachachan/musicblocks,pikurasa/musicblocks