OpenQuake Engine 3.26.2

Release 3.26.2

[Paul Henshaw (@pslh), Paolo Tormene (@ptormene), Antonio Ettorre (@antonioettorre)]

• Fixed install.py to invoke the post installation operations correctly

[Michele Simionato (@micheles)]

• Internal: fixed get_nbytes for empty datasets
• Changed the avg_gmf exporter to export only nonzero values
• Fixed bug in classical_risk from hazard_curves.csv manifesting as a
  KeyError in U32([sid2idx[sid] for sid in df.sid])