Initialize LiveRegs once in BranchFolder::mergeCommonTails
This should fix '(TRI && "LivePhysRegs is not initialized."' assertions
when building the lang/qt5-qml port in certain configurations.
Approved by: re (kib)
Reported by: Piotr Kubaj <pkubaj@anongoth.pl>
PR: 231355
MFC after: 3 days