qt: Fix richtext detection hang issue on very old Qt versions
qt: Fix richtext detection hang issue on very old Qt versions

Alternative implementation. Thanks to @awoland for the original.
Fixes #3486.

Rebased-from: 90a28680bd8b24800428b301f7bf6cbf534de2ca 0.8.x

MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin,MidasPaymentLTD/midascoin