Add protection to fill H_vis_tautau variables

Because of the way the branches are filled, inconsistent dummy values were observed for H_vis_tautau_pt variables:

• -99 in case found_lead_tau=false
• 0 in case found_lead_tau=true but found_tautau_vis=false
• regular values otherwise

This makes dummy values consistent with:

• -99 in case found_tautau_vis=false
• regular values otherwise

FYI @lcadamur @mfujimot @shahzad @pbokan @bmoser