Call existsProviderTxConflict after CheckSpecialTx (#2690)
Call existsProviderTxConflict after CheckSpecialTx (#2690)

Otherwise we might end up passing and invalid proTx into it, causing
assertions to fail and thus crash the process.
nmarley/dash,UdjinM6/dash,UdjinM6/dash,UdjinM6/dash,dashpay/dash,dashpay/dash,dashpay/dash,nmarley/dash,thelazier/dash,thelazier/dash,ionomy/ion,ionomy/ion,dashpay/dash,thelazier/dash,nmarley/dash,ionomy/ion,nmarley/dash,ionomy/ion,UdjinM6/dash,ionomy/ion,nmarley/dash,dashpay/dash,nmarley/dash,UdjinM6/dash,thelazier/dash,ionomy/ion,nmarley/dash,thelazier/dash