MergedPi0Maker creates particles with NaN/Inf values

See LHCb#370 (closed)

We are seeing particles in the location

Basic particle with NAN/INF data found in 'LHCb__Phys__ParticleMakers__MergedPi0Maker_c7605274/Particles'

which fail the new checks added in !4048 (merged)

 inline auto partIsFinite( const LHCb::Particle& p ) {
    return ( std::isfinite( p.momentum().Px() ) && //
             std::isfinite( p.momentum().Py() ) && //
             std::isfinite( p.momentum().Pz() ) && //
             std::isfinite( p.momentum().E() ) );
  }

Whatever is causing this should be fixed to prevent them ever appearing in the output from the algorithm.

FYI @cmarinbe @mveghel