Fix initialization of weights_precision, otherwise the outputs page can not be displayed when the variable is undefined

Author: ptormene

openquake/server/views.py

@@ -1505,6 +1505,7 @@ def web_engine_get_outputs_impact(request, calc_id):
             losses = (f'The risk can not be computed since the hazard is too low:'
                       f' the maximum value of the average GMF is {max_avg_gmf:.5f}')
             losses_header = None
+            weights_precision = None
         else:
             losses_header = [
                 f'{field}<br><i>{FIELD_DESCRIPTION[field]}</i>'