This fixes issue #13755.
FPHSA(XX DEFAULT_MSG XX_FOUND)
always succeeded due to the way how the XX_FOUND variable was set.
It was preset to TRUE, and then reset to FALSE if something was missing
(...which had the effect that XX_FOUND itself was already preset when FPHSA
checked whether XX_FOUND is set)

Now XX_FOUND is unset first, and only later on set to TRUE.

Alex