Work around crash in the QrCodeDecoder

This would need a larger restructuring to be fixed properly.
Instead of returning through emitting a signal, this should go through QFuture.
3 jobs for master in 2 minutes and 36 seconds (queued for 222 minutes and 53 seconds)
Status Name Job ID Coverage
  Test
passed build #134114

00:01:02

passed clazy #134112

00:01:12

passed qmllint #134113

00:00:22