Crash due to zero-size spheroids

[Andrew Benson]

When running new high-res merger trees from Markus Haider, Galacticus crashes due to the presence of zero radius (but finite and non-negligible mass) spheroids.

[Andrew Benson (abenson)]

Problem arises when a host disk/spheroid is completely (i.e. gas+stars) moved to the host spheroid/disk as the result of a satellite merger. The angular momentum of the moved component is adjusted once when the gas is moved and once when the stars are moved. Due to rounding errors this can result in the moved component having zero mass but slightly non-zero angular momentum. This was causing the galaxy to be flagged as unphysical and preventing the structure solver from solving for radius. This could then easily result in a spheroid with zero radius as the result of it being associated with an unphysical disk. The fix is to explicitly force the moved component's angular momentum to zero in such cases.

[Andrew Benson (abenson)]

Fixed by http://bazaar.launchpad.net/~abenson/galacticus/v0.9.1/revision/928 which implements an explicit check after moving mass in the host galaxy - if the disk/spheroid has zero total mass then the angular momentum of that component is reset precisely to zero.